User:Egil/Sandbox/units

Info from units that should be included
are                 100 m^2 litre                1000 cc      The litre was defined in 1901 as the old litre             1.000028 dm^3  space occupied by 1 kg of pure water at l                     liter        the temperature of its maximum density under a pressure of 1 atm. This was supposed to be 1000 cubic cm, but it				      was discovered that the original measurement was off. In 1964, the litre was redefined to be exactly 1000 cubic centimeters. mho                  siemens   Inverse of ohm, hence ohm spelled backward galvat               ampere    Named after Luigi Galvani angstrom             1e-10 m   Convenient for describing molecular sizes xunit                1.00202e-13 meter  Used for measuring wavelengths siegbahn             xunit            of X-rays. It is defined to be					  1|3029.45 of the spacing of calcite planes at 18 degC. It was intended to be exactly 1e-13 m, but was later found to be off slightly. fermi                1e-15 m   Convenient for describing nuclear sizes Nuclear radius is from 1 to 10 fermis barn                 1e-28 m^2  Used to measure cross section for particle physics collision, said to				     have originated in the phrase "big as				      a barn". shed                 1e-24 barn  Defined to be a smaller companion to the barn, but it's too small to be of much use. brewster             micron^2/N  measures stress-optical coef diopter              /m        measures reciprocal of lens focal length fresnel              1e12 Hz   occasionally used in spectroscopy shake                1e-8 sec svedberg             1e-13 s   Used for measuring the sedimentation coefficient for centrifuging. gamma                microgram lambda               microliter spat                 1e12 m    Rarely used for astronomical measurements preece               1e13 ohm m  resistivity planck               J s       action of one joule over one second sturgeon             /henry    magnetic reluctance daraf                1/farad   elastance (farad spelled backwards) leo                  10 m/s^2 poiseuille           N s / m^2  viscosity mayer                J/g K     specific heat mired                / microK  reciprocal color temperature. The name abbreviates micro reciprocal degree. metricounce          25 g mounce                metricounce finsenunit           1e5 W/m^2  Measures intensity of ultraviolet light with wavelength 296.7 nm. fluxunit             1e-26 W/m^2 Hz  Used in radio astronomy to measure the energy incident on the receiving body across a specified frequency bandwidth. [12] jansky               fluxunit  K. G. Jansky identified radio waves coming Jy                   jansky    from outer space in 1931. pfu                 / cm^2 sr s  particle flux unit -- Used to measure rate at which particles are received by				     a spacecraft as particles per solid angle per detector area per second. [18] katal                mol/sec   Measure of the amount of a catalyst. One kat                  katal       katal of catalyst enables the reaction to consume or produce on mol/sec.

minute               60 s min                   minute hour                 60 min hr                   hour day                  24 hr d                     day da                   day week                 7 day wk                   week sennight             7 day fortnight            14 day blink                1e-5 day  Actual human blink takes 1|3 second ce                   1e-2 day cron                 1e6 years watch                4 hours   time a sentry stands watch or a ship's crew is on duty. bell                 1|8 watch  Bell would be sounded every 30 minutes.

circle               2 pi radian degree               1|360 circle arcdeg               degree arcmin               1|60 degree arcminute            arcmin arcsec               1|60 arcmin arcsecond            arcsec quadrant             1|4 circle quintant             1|5 circle sextant              1|6 circle

pulsatance           radian / sec gon                  1|100 rightangle  measure of grade grade                gon centesimalminute     1|100 grade centesimalsecond     1|100 centesimalminute milangle             1|6400 circle    Official NIST definition. Another choice is 1e-3 radian. pointangle           1|32 circle  Used for reporting compass readings centrad              0.01 radian  Used for angular deviation of light through a prism. mas                  milli-arcsec  Used by astronomers seclongitude         circle (seconds/day)  Astronomers measure longitude (which they call right ascension) in				     time units by dividing the equator into 24 hours instead of 360 degrees.

Solid angle measure

sphere               4 pi sr squaredegree          1|180^2 pi^2 sr squareminute          1|60^2 squaredegree squaresecond         1|60^2 squareminute squarearcmin         squareminute squarearcsec         squaresecond sphericalrightangle  0.5 pi sr octant                0.5 pi sr

Concentration measures

percent              0.01 mill                 0.001    Originally established by Congress in 1791 as a unit of money equal to 0.001 dollars, it has come to refer to 0.001 in general. Used by some towns to set their property tax rate, and written with a symbol similar to the % symbol but with two 0's in the denominator. [18] proof                1|200    Alcohol content measured by volume at 60 degrees Fahrenheit. This is a USA measure. In Europe proof=percent. ppm                  1e-6 partspermillion      ppm ppb                  1e-9 partsperbillion      ppb      USA billion ppt                  1e-12 partspertrillion     ppt      USA trillion karat                1|24     measure of gold purity caratgold            karat gammil               mg/l basispoint           0.01 %   Used in finance fine                 1|1000   Measure of gold purity

The pH scale is used to measure the concentration of hydronium (H3O+) ions in a solution. A neutral solution has a pH of 7 as a result of dissociated water molecules.

pH    pH(x) [;mol/liter] 10^(-x) mol/liter ; (-log(pH liters/mol))

Temperature

Two types of units are defined: units for computing temperature differences and functions for converting absolute temperatures. Conversions for differences start with "deg" and conversions for absolute temperature start with "temp".

°F         tempF(x) [;K] (x+(-32)) degF + stdtemp ; (tempF+(-stdtemp))/degF + 32

°K          tempC(x) [;K] x K + stdtemp ; (tempC +(-stdtemp))/K  In 1741 Anders Celsius °C           tempcelsius(x) [;K] tempC(x); ~tempC(tempcelsius)  introduced a temperature degcelsius           K        scale with water boiling at 0 degrees and K       freezing at 100 degrees at standard pressure. After his death the fixed points were reversed and the scale was called the centigrade scale. Due to the difficulty of				  accurately measuring the temperature of				   melting ice at standard pressure, the centigrade scale was replaced in 1954 by				  the Celsius scale which is defined by				   subtracting 273.15 from the temperature in Kelvins. This definition differed slightly from the old centigrade definition, but the Kelvin scale depends on the triple point of				  water rather than a melting point, so it can be measured accurately.

fahrenheit        5|9 degC  Fahrenheit defined his temperature scale 5|9 degC by setting 0 to the coldest temperature he could produce in his lab with a salt water solution and by setting 96 degrees to body heat. In Fahrenheit's words:

Placing the thermometer in a mixture of				     sal ammoniac or sea salt, ice, and water a point on the scale will be found which is denoted as zero. A second point is				     obtained if the same mixture is used without salt. Denote this position as 30. A third point, designated as 96, is				     obtained if the thermometer is placed in				      the mouth so as to acquire the heat of a healthy man." (D. G. Fahrenheit,				      Phil. Trans. (London) 33, 78, 1724)

rankine       degF             The Rankine scale has the degreesrankine  Fahrenheit degree, but it's zero degF            is at absolute zero.

reaumur           10|8 degC  The Reaumur scale was used in Europe and particularly in France. It is defined to be 0 at the freezing point of water and 80 at the boiling point. Reaumur apparently selected 80 because it is divisible by many numbers.

Units cannot handle wind chill or heat index because they are two variable functions, but they are included here for your edification. Clearly these equations are the result of a model fitting operation.

wind chill index (WCI) a measurement of the combined cooling effect of low air temperature and wind on the human body. The index was first defined by the American Antarctic explorer Paul Siple in 1939. As currently used by U.S. meteorologists, the wind chill index is computed from the temperature T (in °F) and wind speed V (in mi/hr) using the formula: WCI = 0.0817(3.71 sqrt(V) + 5.81 - 0.25V)(T - 91.4) + 91.4. For very low wind speeds, below 4 mi/hr, the WCI is actually higher than the air temperature, but for higher wind speeds it is lower than the air temperature.

heat index (HI or HX) a measure of the combined effect of heat and humidity on the human body. U.S. meteorologists compute the index from the temperature T (in °F) and the relative humidity H (as a     value from 0 to 1). HI = -42.379 + 2.04901523 T + 1014.333127 H - 22.475541 TH	    - .00683783 T^2 - 548.1717 H^2 + 0.122874 T^2 H + 8.5282 T H^2 - 0.0199 T^2 H^2.

Physical constants

Basic constants

pi                   3.14159265358979323846 c                    2.99792458e8 m/s  speed of light in vacuum (exact) light                c mu0                   4 pi 1e-7 H/m   permeability of vacuum (exact) epsilon0             1/mu0 c^2       permittivity of vacuum (exact) energy               c^2             convert mass to energy e                   1.602176462e-19 C  electron charge h                  6.62606876e-34 J s  Planck constant hbar                 h / 2 pi spin                  hbar coulombconst         1/4 pi epsilon0  listed as "k" sometimes

Physico-chemical constants

atomicmassunit       1.66053873e-27 kg atomic mass unit (defined to be u                     atomicmassunit    1|12 of the mass of carbon 12) amu                  atomicmassunit amu chem             1.66026e-27 kg  1|16 of the weighted average mass of					    the 3 naturally occuring neutral

isotopes of oxygen amu phys             1.65981e-27 kg  1|16 of the mass of a neutral oxygen 16 atom dalton               u               Maybe this should be amu_chem? avogadro             grams/amu mol   size of a mole N A                  avogadro gasconstant        8.314472 J / mol K  molar gas constant R                    gasconstant boltzmann            R / N_A         Boltzmann constant k                    boltzmann molarvolume      mol R stdtemp / atm  Volume occupied by one mole of an ideal gas at STP. loschmidt  avogadro mol / molarvolume  Molecules per cubic meter of an ideal gas at STP. Loschmidt did work similar to Avogadro. stefanboltzmann pi^2 k^4 / 60 hbar^3 c^2 The power per area radiated by a sigma                 stefanboltzmann   blackbody at temperature T is given by sigma T^4. wiendisplacement     2.8977686e-3 m K  Wien's Displacement Law gives the frequency at which the Planck spectrum has maximum intensity. The relation is lambda T = b where lambda is wavelength, T is					   temperature and b is the Wien displacement. This relation is					   used to determine the temperature of stars. K J 483597.9 GHz/V  Direct measurement of the volt is difficult. Until recently, laboratories kept Weston cadmium cells as a reference, but they could drift. In 1987 the CGPM officially recommended the use of the Josephson effect as a laboratory representation of the volt. The Josephson effect occurs when two superconductors are separated by a thin insulating layer. A "supercurrent" flows across the insulator with a frequency that depends on the potential applied across the superconductors. This frequency can be very accurately measured. The Josephson constant K_J, which is equal to 2e/h, relates the measured frequency to the potential. The value given here is the officially specified value for use beginning in 1990. The 1998 recommended value of the constant is 483597.898 GHz/V. R K 25812.807 ohm   Measurement of the ohm also presents difficulties. The old approach involved maintaining resistances that were subject to drift. The new standard is based on the Hall effect. When a current carrying ribbon is placed in a magnetic field, a potential difference develops across the ribbon. The ratio of the potential difference to the current is called the Hall resistance. Klaus von Klitzing discovered in 1980 that the Hall resistance varies in discrete jumps when the magnetic field is very large and the temperature very low. This enables accurate realization of the resistance h/e^2 in the lab. The value given here is the officially specified value for use beginning in 1990.

Various conventional values

Hg          13.5951 gram force / cm^3  Standard weight of mercury (exact) water                gram force/cm^3  Standard weight of water (exact) waterdensity         gram / cm^3     Density of water

mach                 331.46 m/s      speed of sound in dry air at STP

Atomic constants

Rinfinity            10973731.568 /m  The wavelengths of a spectral series R H                  10967760 /m       can be expressed as 1/lambda = R (1/m^2 - 1/n^2). where R is a number that various slightly from element to element. For hydrogen, R_H is the value, and for heavy elements, the value approaches Rinfinity, which can be					   computed from m_e c alpha^2 / 2 h					   with a loss of 5 digits of precision. alpha                7.297352533e-3  The fine structure constant was introduced to explain fine structure visible in spectral lines. It can be computed from mu0 c e^2 / 2 h					   with a loss of 3 digits precision and loss of precision in derived values which use alpha. bohrradius           alpha / 4 pi Rinfinity prout                185.5 keV       nuclear binding energy equal to 1|12 binding energy of the deuteron Planck constants

planckmass           2.1767e-8 kg    sqrt(hbar c / G) m P                   planckmass plancktime           hbar / planckmass c^2 t P                  plancktime plancklength         plancktime c l P                   plancklength

Masses of elementary particles

electron         5.485799110e-4 u proton            1.00727646688 u neutron           1.00866491578 u muon              0.1134289168 u deuteron          2.01355321271 u alpha particle     4.0015061747 u

particle wavelengths: the compton wavelength of a particle is defined as h / m c where m is the mass of the particle.

Magnetic moments

bohrmagneton         e hbar / 2 electronmass mu B                 bohrmagneton nuclearmagneton      e hbar / 2 protonmass mu N                 nuclearmagneton

Units derived from physical constants kgf                  kg force technicalatmosphere  kgf / cm^2 at                   technicalatmosphere hyl                  kgf s^2 / m  Also gram-force s^2/m according to [15] mmHg                 mm Hg torr                  mmHg    These units, both named after Evangelista tor                      Pa  Torricelli, should not be confused. Acording to [15] the torr is actually atm/760 which is slightly different. inHg                 inch Hg inH2O                 inch water mmH2O                mm water eV                   e V     Energy acquired by a particle with charge e electronvolt          eV        when it is accelerated through 1 V lightyear             c julianyear  The 365.25 day year is specified in				      NIST publication 811 lightsecond          c s lightminute           c min parsec               au / tan(arcsec)   Unit of length equal to distance parsec              from the sun to a point having heliocentric parallax of 1 arcsec (derived from parallax					      second). A distant object with paralax theta will be about (arcsec/theta) parsecs from the sun (using the approximation					      that tan(theta) = theta). rydberg              h c Rinfinity      Rydberg energy crith                0.089885 gram      The crith is the mass of one liter of hydrogen at standard temperature and pressure. amagatvolume         molarvolume amagat               mol/amagatvolume   Used to measure gas densities lorentz              bohrmagneton / h c  Used to measure the extent that the frequency of light is shifted by a magnetic field. cminv                h c / cm           Unit of energy used in infrared invcm                cminv                spectroscopy. wavenumber           cminv kcal mol             kcal / mol N_A     kcal/mol is used as a unit of energy by physical chemists.

CGS system based on centimeter, gram and second

dyne                 cm gram / s^2  force dyn                  dyne erg                  cm dyne        energy poise                gram / cm s    viscosity, honors Jean Poiseuille P                    poise rhe                  /poise         reciprocal viscosity stokes               cm^2 / s       kinematic viscosity St                   stokes stoke                stokes lentor               stokes         old name Gal                  cm / s^2       acceleration, used in geophysics galileo              Gal            for earth's gravitational field (note that "gal" is for gallon					 but "Gal" is the standard symbol					 for the gal which is evidently a					 shortened form of "galileo".) barye                dyne/cm^2      pressure barad                barye          old name kayser               1/cm           Proposed as a unit for wavenumber balmer               kayser         Even less common name than "kayser" kine                 cm/s           velocity bole                 g cm / s       momentum pond                 gram force glug             gram force s^2 / cm  Mass which is accelerated at					   1 cm/s^2 by 1 gram force darcy        centipoise cm^2 / s atm  Measures permeability to fluid flow.

One darcy is the permeability of a					  medium that allows a flow of cc/s of a liquid of centipoise viscosity under a pressure gradient of atm/cm. Named for H. Darcy.

mohm                 cm / dyn s     mobile ohm, measure of mechanical mobileohm            mohm             mobility mechanicalohm        dyn s / cm     mechanical resistance acousticalohm        dyn s / cm^5   ratio of the sound pressure of					   1 dyn/cm^2 to a source of strength 1 cm^3/s ray                  acousticalohm rayl                 dyn s / cm^3   Specific acoustical resistance eotvos               1e-9 Gal/cm    Change in gravitational acceleration over horizontal distance

Electromagnetic units derived from the abampere

abampere             10 A           Current which produces a force of abamp                 abampere         2 dyne/cm between two infinitely aA                   abampere         long wires that are 1 cm apart biot                 aA             alternative name for abamp Bi                   biot abcoulomb            abamp sec abcoul               abcoulomb abfarad              abampere sec / abvolt abhenry              abvolt sec / abamp abvolt               dyne cm / abamp sec abohm                abvolt / abamp abmho                /abohm gauss                abvolt sec / cm^2 Gs                   gauss maxwell              abvolt sec     Also called the "line" Mx                   maxwell oersted              gauss / mu0 Oe                   oersted gilbert              gauss cm / mu0 Gb                   gilbert Gi                   gilbert unitpole             4 pi maxwell emu                  erg/gauss  "electro-magnetic unit", a measure of 				    magnetic moment, often used as emu/cm^3 to specify magnetic moment density.

Gaussian system: electromagnetic units derived from statampere.

Note that the Gaussian units are often used in such a way that Coulomb's law has the form F= q1 * q2 / r^2. The constant 1|4*pi*epsilon0 is incorporated into the units. From this, we can get the relation force=charge^2/dist^2. This means that the simplification esu^2 = dyne cm^2 can be used to simplify units in the Gaussian system, with the curious result that capacitance can be measured in cm, resistance in sec/cm, and inductance in sec^2/cm. These units are given the names statfarad, statohm and stathenry below.

statampere           10 A cm / s c statamp               statampere statvolt             dyne cm / statamp sec statcoulomb          statamp s esu                   statcoulomb statcoul             statcoulomb statfarad            statamp sec / statvolt cmcapacitance        statfarad stathenry            statvolt sec / statamp statohm              statvolt / statamp statmho              /statohm statmaxwell          statvolt sec franklin             statcoulomb debye                1e-18 statcoul cm  unit of electrical dipole moment helmholtz            debye/angstrom^2  Dipole moment per area jar                  1000 statfarad   approx capacitance of Leyden jar

Some historical eletromagnetic units

intampere            0.999835 A   Defined as the current which in one intamp               intampere      second deposits .001118 gram of					 silver from an aqueous solution of silver nitrate. intfarad             0.999505 F intvolt               1.00033 V intohm                1.000495 ohm  Defined as the resistance of a					 uniform column of mercury containing 14.4521 gram in a column 1.063 m long and maintained at 0 degC. daniell              1.042 V      Meant to be electromotive force of a					 Daniell cell, but in error by .04 V faraday               N_A e mol    Charge that must flow to deposit or faraday phys          96521.9 C      liberate one gram equivalent of  any faraday chem         96495.7 C      element. (The chemical and physical					 values are off slightly from what is					 obtained by multiplying by amu_chem					 or amu_phys. These values are from					 a 1991 NIST publication.)  Note that there is a Faraday constant which is					 equal to N_A e and hence has units of C/mol. kappline             6000 maxwell  Named by and for Gisbert Kapp siemensunit          0.9534 ohm   Resistance of a meter long column of mercury with a 1 mm cross section.

Photometric units

candle               1.02 candela  Standard unit for luminous  intensity hefnerunit           0.9 candle     in use before candela hefnercandle         hefnerunit violle               20.17 cd     luminous intensity of 1 cm^2 of					 platinum at its temperature of					 solidification (2045 K)

lumen                cd sr        Luminous flux (luminous energy per lm                    lumen           time unit)

talbot               lumen s      Luminous energy lumberg              talbot

lux                  lm/m^2       Illuminance or exitance (luminous lx                    lux            flux incident on or coming from phot                  lumen / cm^2   a surface) ph                   phot footcandle           lumen/ft^2   Illuminance from a 1 candela source at a distance of one foot metercandle          lumen/m^2    Illuminance from a 1 candela source at a distance of one meter

mcs                  metercandle s  luminous energy per area, used to					  measure photographic exposure

nox                  1e-3 lux     These two units were proposed for skot                 1e-3 apostilb  measurements relating to dark adapted eyes. Luminance measures

nit                  cd/m^2       Luminance: the intensity per projected stilb                cd / cm^2    area of an extended luminous source. sb                   stilb        (nit is from latin nitere = to shine.)

apostilb             cd/pi m^2 asb                  apostilb blondel              apostilb     Named after a French scientist.

Equivalent luminance measures. These units are units which measure the luminance of a surface with a specified exitance which obeys Lambert's law. (Lambert's law specifies that luminous intensity of a perfectly diffuse luminous surface is proportional to the cosine of the angle at which you view the luminous surface.)

equivalentlux        cd / pi m^2  luminance of a 1 lux surface equivalentphot       cd / pi cm^2  luminance of a 1 phot surface lambert              cd / pi cm^2 footlambert          cd / pi ft^2

The bril is used to express "brilliance" of a source of light on a logarithmic scale to correspond to subjective perception. An increase of 1 bril means doubling the luminance. A luminance of 1 lambert is defined to have a brilliance of 1 bril.

bril        bril(x) [;lambert] 2^(x+-100) lamberts  ;log2(bril/lambert)+100

Some luminance data from the IES Lighting Handbook, 8th ed, 1993

sunlum               1.6e9 cd/m^2  at zenith sunillum             100e3 lux    clear sky sunillum o           10e3 lux     overcast sky sunlum h             6e6 cd/m^2   value at horizon skylum               8000 cd/m^2  average, clear sky skylum o             2000 cd/m^2  average, overcast sky moonlum              2500 cd/m^2

Photographic Exposure Value

The Additive Photographic EXposure (APEX) system developed in Germany in the 1960s was an attempt to simplify exposure determination for people who relied on exposure tables rather than exposure meters. Shortly thereafter, nearly all cameras incorporated exposure meters, so the APEX system never caught on, but the concept of Exposure Value (EV) given by

A^2  LS   ES     2^EV = --- = -- = -- T   K    C

Where A = Relative aperture (f-number) T = Shutter time in seconds L = Scene luminance in cd/m2 E = Scene illuminance in lux S = Arithmetic ISO film speed K = Reflected-light meter calibration constant C = Incident-light meter calibration constant

remains in use. Strictly speaking, an Exposure Value is a combination of aperture and shutter time, but it's also commonly used to indicate luminance (or illuminance). Conversion to luminance or illuminance units depends on the ISO film speed and the meter calibration constant. Common practice is to use an ISO film speed of 100 (because film speeds are in even 1/3-step increments, the exact value is 64 * 2^(2|3)). Calibration constants vary among camera and meter manufacturers: Canon, Nikon, and Sekonic use a value of 12.5 for reflected-light meters, while Minolta and Pentax use a value of 14. Minolta and Sekonic use a value of 250 for incident-light meters with flat receptors.

s100                 64 * 2^(2|3) / lx s    exact speed for ISO 100 film Reflected-light meter calibration constant with ISO 100 film

k1250                12.5 (cd/m2) / lx s    For Canon, Nikon, and Sekonic k1400                14 (cd/m2) / lx s      For Minolta and Pentax

Incident-light meter calibration constant with ISO 100 film

c250                 250 lx / lx s          flat-disc receptor

Exposure value to scene luminance with ISO 100 film

For Minolta or Pentax ev100(x) [;cd/m^2] 2^x k1400 / s100; log2(ev100 s100 / k1400) For Canon, Nikon or Sekonic ev100     ev100(x) [;cd/m^2] 2^x k1250 / s100; log2(ev100 s100 / k1250)

Exposure value to scene illuminance with ISO 100 film

iv100     iv100(x) [1;lx] 2^x c250 / s100; log2(iv100 s100 / c250)

Astronomical time measurements

Astronmical time measurement is a complicated matter. The rotation of the earth and motion of the planets is not uniform. Originally the second was defined relative to the "mean solar day". It is necessary to use the mean day because the earth's orbit is elliptical so the length of the day varies throughout the year. Simon Newcomb discovered that there were significant irregularities in the rotation of the earth and he came up with equations using the location of a fictitious mean sun. The length of the second was determined from the tropical year obtained from Newcomb's equations. This second was officially used from 1960 to 1967, at which point atomic clocks replaced astronomical measurements for a standard of time.

The measures that appear below are probably obtained from an "ephemeris" which is a set of equations that predicts the locations of the planets over time.

anomalisticyear      365.2596 days      The time between successive perihelion passages of the earth. siderealyear         365.256360417 day  The time for the earth to make one revolution around the sun relative to the stars. tropicalyear         365.242198781 day  The mean interval between vernal equinoxes. Differs from the sidereal year by 1 part in					      26000 due to precession of the earth about its rotational axis combined with precession of the perihelion of the earth's orbit. gaussianyear         365.2690 days      The orbital period of a body in					       circular orbit at a distance of 1 au from the sun. Calculated from Kepler's third law. elipseyear           346.62 days        The line of nodes is the intersection of the plane of					      Earth's orbit around the sun with the plane of the moon's orbit around earth. Eclipses can only occur when the moon and sun are close to this line. The line rotates and appearances of the sun on the line of nodes occur every eclipse year. saros                223 synodicmonth   The earth, moon and sun appear in					       the same arrangement every saros, so if an eclipse occurs, then one saros later, a similar eclipse will occur. (The saros					      is close to 19 eclipse years.) The eclipse will occur about 120 degrees west of the preceeding one because the saros is not an even number of days. After 3 saros, an					      eclipse will occur at approximately the same place. siderealday          23.934469444 hour  The sidereal day is the interval siderealhour         1|24 siderealday     between two successive transits siderealminute       1|60 siderealhour    of a star over the meridian, siderealsecond       1|60 siderealminute  or the time required  for the earth to make one rotation relative to the stars. The more usual solar day is the time required to make a rotation relative to the sun. Because the earth moves in its orbit, it has to turn a bit extra to face the sun again, hence the solar day is slightly longer. anomalisticmonth     27.55454977 day    Time for the moon to travel from perigee to perigee nodicalmonth         27.2122199 day     The nodes are the points where draconicmonth        nodicalmonth         an orbit crosses the ecliptic. draconiticmonth      nodicalmonth         This is the time required to					       travel from the ascending node to the next ascending node. siderealmonth        27.321661 day      Time required for the moon to					       orbit the earth lunarmonth           29 days+12 hours+44 minutes+2.8 seconds Time between full moons. Full synodicmonth         lunarmonth           moon occur when the sun and lunation             synodicmonth         moon are on opposite sides of lune                  1|30 lunation        the earth. Since the earth lunour               1|24 lune            moves around the sun, the moon has to revolve a bit farther to					      get into the full moon configuration. year                 tropicalyear yr                   year month                1|12 year mo                   month lustrum              5 years            The Lustrum was a Roman purification ceremony that took place every five years. Classically educated Englishmen used this term. decade               10 years century              100 years millennium           1000 years millennia            millennium solaryear            year lunaryear            12 lunarmonth calendaryear         365 day commonyear           365 day leapyear             366 day julianyear           365.25 day gregorianyear        365.2425 day islamicyear          354 day         A year of 12 lunar months. They islamicleapyear      355 day         began counting on July 16, AD 622 when Muhammad emigrated to Medina (the year of the Hegira). They need 11 leap days in 30 years to stay in					 sync with the lunar year which is a					  bit longer than the 29.5 days of the average month. The months do not keep to the same seasons, but regress through the seasons every 32.5 years. islamicmonth         1|12 islamicyear  They have 29 day and 30 day months.

The Hewbrew year is also based on lunar months, but synchronized to the solar calendar. The months vary irregularly between 29 and 30 days in length, and the years likewise vary. The regular year is 353, 354, or 355 days long. To keep up with the solar calendar, a leap month of 30 days is inserted every 3rd, 6th, 8th, 11th, 14th, 17th, and 19th years of a 19 year cycle. This gives leap years that last 383, 384, or 385 days.

The Hartree system of atomic units, derived from fundamental units of mass (of electron), action (planck's constant), charge, and the coulomb constant.

Fundamental units

atomicmass           electronmass atomiccharge         e atomicaction          hbar

derived units (Warning: accuracy is lost from deriving them this way)

atomiclength         bohrradius atomictime           hbar^3/coulombconst^2 atomicmass e^4  Period of first bohr orbit atomicvelocity       atomiclength / atomictime atomicenergy         hbar / atomictime hartree              atomicenergy Hartree              hartree

These thermal units treat entropy as charge, from [5]

thermalcoulomb       J/K       entropy thermalampere        W/K       entropy flow thermalfarad         J/K^2 thermalohm           K^2/W     thermal resistance fourier              thermalohm thermalhenry         J K^2/W^2  thermal inductance thermalvolt          K         thermal potential difference

United States units

linear measure

The US Metric Law of 1866 gave the exact relation 1 meter = 39.37 inches. From 1893 until 1959, the foot was exactly 1200|3937 meters. In 1959 the definition was changed to bring the US into agreement with other countries. Since then, the foot has been exactly 0.3048 meters. At the same time it was decided that any data expressed in feet derived from geodetic surveys within the US would continue to use the old definition.

U.S.                   1200|3937 m/ft  These four values will convert US-                    US                  international measures to survey-                 US                  US Survey measures geodetic-              US int                   3937|1200 ft/m  Convert US Survey measures to int-                    int                 international measures

inch                 2.54 cm in                    inch foot                 12 inch feet                 foot ft                   foot yard                 3 ft yd                    yard mile                 5280 ft         The mile was enlarged from 5000 ft					  to this number in order to make it an even number of furlongs. (The Roman mile is 5000 romanfeet.) line                 1|12 inch  Also defined as '.1 in' or as '1e-8 Wb' rod (unit)                  5.5 USyard perch                rod furlong              40 rod          From "furrow long" statutemile          USmile league               3 USmile        Intended to be an an hour's walk

surveyor's measure

surveyorschain       66 surveyft surveyorspole        1|4 surveyorschain surveyorslink        1|100 surveyorschain chain                surveyorschain surveychain          chain ch                   chain link                 surveyorslink acre                 10 chain^2 intacre              43560 ft^2  Acre based on international ft acrefoot              acre surveyfoot section              USmile^2 township             36 section homestead            160 acre  Area of land granted by the 1862 Homestead Act of the United States Congress gunterschain         surveyorschain

engineerschain       100 ft engineerslink         1|100 engineerschain ramsdenschain        engineerschain ramsdenslink         engineerslink

nautical measure

fathom               6 USft  Originally defined as the distance from fingertip to fingertip with arms fully extended. nauticalmile         1852 m  Supposed to be one minute of latitude at the equator. That value is about 1855 m.				 Early estimates of the earth's circumference were a bit off. The value of 1852 m was made the international standard in 1929. The US did not accept this value until 1954. The UK switched in 1970.

cable                1|10 nauticalmile intcable             cable             international cable cablelength          cable UScable              100 fathom navycablelength      720 USft          used for depth in water marineleague         3 nauticalmile geographicalmile     brnauticalmile knot                 nauticalmile / hr click                 km

Avoirdupois weight

pound                0.45359237 kg  The one normally used lb                   pound          From the latin libra grain                1|7000 pound   The grain is the same in all three weight systems. It was originally defined as the weight of a barley corn taken from the middle of the ear. ounce                1|16 pound oz                   ounce dram                 1|16 ounce dr                   dram ushundredweight      100 pounds cwt                  hundredweight shorthundredweight   ushundredweight uston                shortton shortton             2000 lb quarterweight         1|4 uston shortquarterweight   1|4 shortton shortquarter         shortquarterweight

Troy Weight. In 1828 the troy pound was made the first United States standard weight. It was to be used to regulate coinage.

troypound            5760 grain troyounce            1|12 troypound ozt                  troyounce pennyweight          1|20 troyounce  Abbreviated "d" in reference to a dwt                   pennyweight      Frankish coin called the "denier" minted in the late 700's. There were 240 deniers to the pound. assayton             mg ton / troyounce  mg / assayton = troyounce / ton usassayton           mg uston / troyounce brassayton           mg brton / troyounce

Some other jewelers units

metriccarat          0.2 gram       Defined in 1907 metricgrain          50 mg carat                 metriccarat ct                   carat jewelerspoint        1|100 carat silversmithpoint     1|4000 inch

Apothecaries' weight

appound              troypound apounce              troyounce apdram               1|8 apounce apscruple            1|3 apdram

Liquid measure

gal                  gallon quart                1|4 gallon pint                 1|2 quart gill                 1|4 pint usgallon             231 in^3 usquart              1|4 usgallon uspint               1|2 usquart usgill               1|4 uspint usfluidounce         1|16 uspint fluiddram            1|8 usfloz minimvolume          1|60 fluiddram qt                   quart pt                   pint floz                 fluidounce usfloz               usfluidounce fldr                 fluiddram liquidbarrel         31.5 usgallon usbeerbarrel         2 beerkegs beerkeg              15.5 usgallon  Various among brewers

ponykeg              1|2 beerkeg winekeg              12 usgallon petroleumbarrel      42 usgallon    Originated in Pennsylvania oil barrel               petroleumbarrel  fields, from the winetierce bbl                  barrel hogshead             2 liquidbarrel usfirkin             9 gallon

Dry measures: The Winchester Bushel was defined by William III in 1702 and legally adopted in the US in 1836.

usbushel             2150.42 in^3  Volume of 8 inch cylinder with 18.5 bu                   bushel       inch diameter (rounded) peck                 1|4 bushel uspeck               1|4 usbushel brpeck               1|4 brbushel pk                   peck drygallon            1|2 uspeck dryquart             1|4 drygallon drypint              1|2 dryquart drybarrel            7056 in^3    Used in US for fruits, vegetables, and other dry commodities except for cranberries. cranberrybarrel      5826 in^3    US cranberry barrel heapedbushel         1.278 usbushel Why this particular value? Often rounded to 1.25 bushels.

Grain measures. The bushel as it is used by farmers in the USA is actually a measure of mass which varies for different commodities. Canada uses the same bushel masses for most commodities, but not for oats.

wheatbushel          60 lb soybeanbushel         60 lb cornbushel            56 lb ryebushel             56 lb barleybushel          48 lb oatbushel             32 lb

ricebushel           45 lb canada oatbushel      34 lb

Wine and Spirits measure

ponyvolume           1 usfloz jigger               1.5 usfloz  Can vary between 1 and 2 usfloz shot                 jigger    Sometimes 1 usfloz eushot               25 ml     EU standard spirits measure fifth                1|5 usgallon winebottle           750 ml    US industry standard, 1979 winesplit            1|4 winebottle wineglass            4 usfloz magnum               1.5 liter  Standardized in 1979, but given as 2 qt in some references metrictenth          375 ml metricfifth           750 ml metricquart           1 liter

French champagne bottle sizes

split                200 ml jeroboam              2 magnum rehoboam             3 magnum methuselah           4 magnum salmanazar           6 magnum balthazar            8 magnum nebuchadnezzar       10 magnum

Water is "hard" if it contains various minerals, expecially calcium carbonate.

clarkdegree  1|70000      Content by weigh of calcium carbonate gpg          grains/gallon  Divide by water's density to convert to				 a dimensionless concentration measure

Shoe measures

shoeiron             1|48 inch   Used to measure leather in soles shoeounce            1|64 inch   Used to measure non-sole shoe leather

USA shoe sizes. These express the length of the shoe or the length of the "last", the form that the shoe is made on.

shoesize delta       1|3 inch    USA shoe sizes differ by this amount shoe men0            8.25 inch shoe women0          (7+11|12) inch shoe boys0           (3+11|12) inch shoe girls0          (3+7|12) inch

European shoe size. According to     http://www.shoeline.com/footnotes/shoeterm.shtmlparis points

sizes in Europe are measured with Paris points which simply measure the length of the shoe.

europeshoesize       2|3 cm

USA slang units

buck                 US$ fin                  5 US$ sawbuck              10 US$ grand                1000 US$ greenback            US$ key                  kg          usually of marijuana, 60's lid                   1 oz        Another 60's weed unit footballfield        100 yards marathon             26 miles + 385 yards

British

UK                   1200000|3937014 m/ft  The UK lengths were defined by british-                UK                     a bronze bar manufactured in UK-                     UK                     1844. Measurement of that bar revealed the dimensions given here.

brnauticalmile       6080 ft              Used until 1970 when the UK brknot                brnauticalmile / hr  switched to the international brcable              1|10 brnauticalmile  nautical mile. admiraltymile        brnauticalmile admiraltyknot        brknot admiraltycable       brcable seamile              6000 ft shackle               15 fathoms           Adopted 1949 by British navy

British Imperial weight is mostly the same as US weight. A few extra units are added here.

clove                7 lb   stone                 14 lb tod                   28 lb brquarterweight       1|4 brhundredweight brhundredweight      8 stone longhundredweight    brhundredweight long ton             20 brhundredweight brton                long_ton

British Imperial volume measures

brminim              1|60 brdram brscruple            1|3 brdram fluidscruple         brscruple brdram               1|8 brfloz brfluidounce         1|20 brpint brfloz               brfluidounce brgill               1|4 brpint brpint               1|2 brquart brquart              1|4 brgallon brgallon             4.54609 l     The British Imperial gallon was defined in 1824 to be the volume of					water which weighed 10 pounds at 62 deg F with a pressure of 30 inHg. In					1963 it was defined to be the volume occupied by 10 pounds of distilled water of density 0.998859 g/ml weighed in air of density 0.001217 g/ml against weights of density 8.136 g/ml. This gives a value of approximately 4.5459645 liters, but the old liter was in force at this time. In 1976 the definition was changed to exactly 4.54609 liters using the new definition of the liter (1 dm^3). brbarrel             36 brgallon   Used for beer brbushel             8 brgallon brheapedbushel       1.278 brbushel brquarter            8 brbushel brchaldron           36 brbushel

Units derived from imperial system

ouncedal             oz ft / s^2    force which accelerates an ounce at 1 ft/s^2 poundal              lb ft / s^2    same thing for a pound tondal               ton ft / s^2   and for a ton pdl                  poundal psi                  pound force / inch^2 psia                 psi            absolute pressure tsi                  ton force / inch^2 reyn                 psi sec slug                 lbf s^2 / ft slugf                 slug force slinch               lbf s^2 / inch  Mass unit derived from inch second slinchf              slinch force     pound-force system. Used in space applications where in/sec^2 was a natural acceleration measure. geepound             slug lbf                  lb force tonf                 ton force lbm                  lb kip                   1000 lbf    from kilopound ksi                  kip / in^2 mil                  0.001 inch thou                 0.001 inch circularinch         1|4 pi in^2  area of a one-inch diameter circle circularmil          1|4 pi mil^2  area of one-mil diameter circle cmil                 circularmil cental               100 pound centner              cental caliber              0.01 inch   for measuring bullets duty                 ft lbf celo                 ft / s^2 jerk                 ft / s^3 australiapoint       0.01 inch   The "point" is used to measure rainfall in Australia sabin                ft^2        Measure of sound absorption equal to the absorbing power of one square foot of a perfectly absorbing material. The sound absorptivity of an object is the area times a dimensionless absorptivity coefficient. standardgauge       4 ft + 8.5 in  Standard width between railroad track flag                5 ft^2       Construction term referring to sidewalk. rollwallpaper       30 ft^2      Area of roll of wall paper fillpower           in^3 / ounce  Density of down at standard pressure. The best down has 750-800 fillpower. pinlength           1|16 inch    A 17 pin is 17/16 in long in the USA. buttonline          1|40 inch    The line was used in 19th century USA to measure width of buttons. scoopnumber         /quart       Ice cream scoops are labeled with a					number specifying how many scoops fill a quart. beespace            1|4 inch     Bees will fill any space that is smaller than the bee space and leave open spaces that are larger. The size of the space varies with species. diamond             8|5 ft       Marking on US tape measures that is					useful to carpenters who wish to place five studs in an 8 ft distance. Note that the numbers appear in red every 16 inches as well, giving six divisions in 8 feet. retmaunit           1.75 in      Height of rack mountable equipment. U                   retmaunit      Equipment should be 1|32 inch narrower than its U measurement indicates to					allow for clearance, so 4U=(6+31|32)in

Other units of work, energy, power, etc

Calories: energy to raise a gram of water one degree celsius

cal IT               4.1868 J    International Table calorie cal th               4.184 J     Thermochemical calorie cal fifteen          4.18580 J   Energy to go from 14.5 to 15.5 degC cal twenty           4.18190 J   Energy to go from 19.5 to 20.5 degC cal mean             4.19002 J   1|100 energy to go from 0 to 100 degC calorie              cal_IT cal                  calorie calorie IT           cal_IT thermcalorie         cal_th calorie th           thermcalorie Calorie              kilocalorie  the food Calorie thermie           1e6 cal_fifteen  Heat required to raise the temperature of a tonne of water from 14.5 to 15.5 degC.

btu definitions: energy to raise a pound of water 1 degF

btu                  cal lb degF / gram K  international table BTU britishthermalunit   btu btu IT               btu btu th               cal_th lb degF / gram K btu mean              cal_mean lb degF / gram K quad                  quadrillion btu

ECtherm              1.05506e8 J   Exact definition, close to 1e5 btu UStherm              1.054804e8 J  Exact definition therm                UStherm toe                  1e10 cal_IT   ton oil equivalent. Energy released by burning one metric ton of oil. [18] tonscoal             1|2.3 toe     Energy in metric ton coal from [18]. naturalgas           toe / 1270 m^3  Energy released from natural gas from [18]. (At what pressure?)

Celsius heat unit: energy to raise a pound of water 1 degC

celsiusheatunit      cal lb degC / gram K chu                   celsiusheatunit

The horsepower is supposedly the power of one horse pulling. Obviously different people had different horses.

ushorsepower         550 foot pound force / sec  Invented by James Watt hp                   horsepower metrichorsepower     75 kilogram force meter / sec electrichorsepower   746 W boilerhorsepower      9809.50 W waterhorsepower       746.043 W brhorsepower          745.70 W donkeypower           250 W

Thermal insulance: Thermal conductivity has dimension power per area per (temperature difference per length thickness) which comes out to W / K m. If the thickness is fixed, then the conductance will have units of W / K m^2. Thermal insulance is the reciprocal.

Rvalue               degF ft^2 hr / btu Uvalue               1/Rvalue europeanUvalue       watt / m^2 K RSI                   degC m^2 / W clo                   0.155 degC m^2 / W  Supposed to be the insulance required to keep a resting person comfortable indoors. The value given is from NIST and the CRC, but [5] gives a slightly different value of 0.875 ft^2 degF hr / btu. tog                  0.1 degC m^2 / W  Also used for clothing.

Misc other measures

ENTROPY                ENERGY / TEMPERATURE clausius             1e3 cal/K      A unit of physical entropy langley              thermcalorie/cm^2   Used in radiation theory poncelet             100 kg force m / s tonrefrigeration      ton 144 btu / lb day  One ton refrigeration is					 the rate of heat extraction required turn one ton of water to ice in a day. Ice is defined to have a latent heat of 144 btu/lb. tonref               tonrefrigeration refrigeration        tonref / ton frigorie             1000 cal_fifteen Used in refrigeration engineering. tnt                  1e9 cal_th / ton So you can write tons-tnt. This is a defined, not measured, value. airwatt              8.5 (ft^3/min) inH2O  Measure of vacuum power as pressure times air flow.

Permeability: The permeability or permeance, n, of a substance determines how fast vapor flows through the substance. The formula W = n A dP holds where W is the rate of flow (in mass/time), n is the permeability, A is the area of the flow path, and dP is the vapor pressure difference.

perm 0C              grain / hr ft^2 inHg perm zero            perm_0C perm 0               perm_0C perm                 perm_0C perm 23C             grain / hr ft^2 in Hg23C perm twentythree     perm_23C

Counting measures

pair                 2 brace (grouping))    2 nest                  3    often used for items like bowls that 				 nest together hattrick              3    Used in sports, especially cricket and ice				 hockey to report the number of goals. dicker                10 dozen                 12 bakersdozen           13 score                 20 flock                 40 timer                 40 shock                 60 gross                 144 greatgross            12 gross tithe                 1|10  From Anglo-Saxon word for tenth

Paper counting measure

shortquire           24 quire                25 shortream            480 ream                 500 perfectream          516 bundle               2 reams bale                 5 bundles

Paper measures

pointthickness       mil

The metric paper sizes are defined so that if a sheet is cut in half along the short direction, the result is two sheets which are similar to the original sheet. This means that for any metric size, the long side is close to sqrt(2) times the length of the short side. Each series of sizes is generated by repeated cuts in half, with the values rounded down to the nearest millimeter.

A6paper              105 mm 148 mm A7paper                74 mm 105 mm A8paper                52 mm 74 mm A9paper                37 mm 52 mm A10paper               26 mm 37 mm

B0paper             1000 mm 1414 mm  The basic B size has an area B1paper              707 mm 1000 mm  of sqrt(2) square meters. B2paper              500 mm 707 mm B3paper               353 mm 500 mm B4paper               250 mm 353 mm B5paper               176 mm 250 mm B6paper               125 mm 176 mm B7paper                88 mm 125 mm B8paper                62 mm 88 mm B9paper                44 mm 62 mm B10paper               31 mm 44 mm

C0paper              917 mm 1297 mm  The basic C size has an area C1paper              648 mm 917 mm   of sqrt(sqrt(2)) square meters. C2paper              458 mm 648 mm C3paper               324 mm 458 mm   Intended for envelope sizes C4paper              229 mm 324 mm C5paper               162 mm 229 mm C6paper               114 mm 162 mm C7paper                81 mm 114 mm C8paper                57 mm 81 mm C9paper                40 mm 57 mm C10paper               28 mm 40 mm

gsm (Grams per Square Meter), a sane, metric paper weight measure

gsm                  grams / meter^2

In the USA, a collection of crazy historical paper measures are used. Paper is measured as a weight of a ream of that particular type of paper. This is sometimes called the "substance" or "basis" (as in "substance 20" paper). The standard sheet size or "basis size" varies depending on the type of paper. As a result, 20 pound bond paper and 50 pound text paper are actually about the same weight. The different sheet sizes were historically the most convenient for printing or folding in the different applications. These different basis weights are standards maintained by American Society for Testing Materials (ASTM) and the American Forest and Paper Association (AF&PA).

poundbookpaper       lb / 25 inch 38 inch ream lbbook               poundbookpaper poundtextpaper       poundbookpaper lbtext               poundtextpaper poundoffsetpaper     poundbookpaper   For offset printing lboffset             poundoffsetpaper poundbiblepaper      poundbookpaper   Designed to be lightweight, thin, lbbible              poundbiblepaper  strong and opaque. poundtagpaper        lb / 24 inch 36 inch ream lbtag                poundtagpaper poundbagpaper        poundtagpaper lbbag                poundbagpaper poundnewsprintpaper  poundtagpaper lbnewsprint          poundnewsprintpaper poundposterpaper     poundtagpaper lbposter             poundposterpaper poundtissuepaper     poundtagpaper lbtissue             poundtissuepaper poundwrappingpaper   poundtagpaper lbwrapping           poundwrappingpaper poundwaxingpaper     poundtagpaper lbwaxing             poundwaxingpaper poundglassinepaper   poundtagpaper lbglassine           poundglassinepaper poundcoverpaper      lb / 20 inch 26 inch ream lbcover              poundcoverpaper poundindexpaper      lb / 25.5 inch 30.5 inch ream lbindex              poundindexpaper poundbondpaper       lb / 17 inch 22 inch ream  Bond paper is stiff and lbbond               poundbondpaper            durable for repeated poundwritingpaper    poundbondpaper            filing, and it resists lbwriting            poundwritingpaper         ink penetration. poundledgerpaper     poundbondpaper lbledger             poundledgerpaper poundcopypaper       poundbondpaper lbcopy               poundcopypaper poundblottingpaper   lb / 19 inch 24 inch ream lbblotting           poundblottingpaper poundblankspaper     lb / 22 inch 28 inch ream lbblanks             poundblankspaper poundpostcardpaper   lb / 22.5 inch 28.5 inch ream lbpostcard           poundpostcardpaper poundweddingbristol  poundpostcardpaper lbweddingbristol     poundweddingbristol poundbristolpaper    poundweddingbristol lbbristol            poundbristolpaper poundboxboard        lb / 1000 ft^2 lbboxboard           poundboxboard poundpaperboard      poundboxboard lbpaperboard         poundpaperboard

When paper is marked in units of M, it means the weight of 1000 sheets of the given size of paper. To convert this to paper weight, divide by the size of the paper in question.

paperM               lb / 1000

Printing

fournierpoint        0.1648 inch / 12  First definition of the printers point made by Pierre Fournier who defined it in 1737 as 1|12 of a cicero which was 0.1648 inches. olddidotpoint        1|72 frenchinch  François Ambroise Didot, one of					   a family of printers, changed Fournier's definition around 1770 to fit to the French units then in use. bertholdpoint        1|2660 m         H. Berthold tried to create a					   metric version of the didot point in 1878. INpoint              0.4 mm           This point was created by a					   group directed by Fermin Didot in					   1881 and is associated with the imprimerie nationale. It doesn't seem to have been used much. germandidotpoint     0.376065 mm      Exact definition appears in DIN 16507, a German standards document of 1954. Adopted more broadly in 1966 by ??? metricpoint          3|8 mm           Proposed in 1977 by Eurograf point                1|72.27 inch     The American point was invented printerspoint        point            by Nelson Hawks in 1879 and dominates USA publishing. It was standardized by the American Typefounders Association at the value of 0.013837 inches exactly. Knuth uses the approximation given here (which is very close). The comp.fonts FAQ claims that this value is supposed to be 1|12 of a					  pica where 83 picas is equal to 35 cm. But this value differs from the standard. texscaledpoint       1|65536 point    The TeX typesetting system uses texsp                texscaledpoint   this for all computations. computerpoint        1|72 inch        The American point was rounded computerpica         12 computerpoint  to an even 1|72 inch by computer postscriptpoint      computerpoint    people at some point. pspoint              postscriptpoint Q                    1|4 mm           Used in Japanese phototypesetting Q is for quarter frenchprinterspoint  olddidotpoint didotpoint           germandidotpoint  This seems to be the dominant value europeanpoint        didotpoint       for the point used in Europe cicero               12 didotpoint

stick                2 inches

Type sizes

excelsior            3 point brilliant            3.5 point diamondtype          4 point pearl                5 point agate                5.5 point  Originally agate type was 14 lines per inch, giving a value of 1|14 in. ruby                 agate     British nonpareil            6 point mignonette           6.5 point emerald              mignonette  British minion               7 point brevier              8 point bourgeois            9 point longprimer           10 point smallpica            11 point pica                 12 point english      14 point columbian            16 point greatprimer          18 point paragon              20 point meridian             44 point canon                48 point

German type sizes

nonplusultra         2 didotpoint brillant             3 didotpoint diamant              4 didotpoint perl                 5 didotpoint nonpareille          6 didotpoint kolonel              7 didotpoint petit                8 didotpoint borgis               9 didotpoint korpus               10 didotpoint corpus               korpus garamond             korpus mittel               14 didotpoint tertia               16 didotpoint text                 18 didotpoint kleine kanon         32 didotpoint kanon                36 didotpoint grobe kanon          42 didotpoint missal               48 didotpoint kleine sabon         72 didotpoint grobe sabon          84 didotpoint

Information theory units. Note that the name "entropy" is used both to measure information and as a physical quantity.

nat                  ln(2) bits          Entropy measured base e

hartley              log2(10) bits       Entropy of a uniformly distributed random variable over 10 symbols.

Computer

bps                  bit/sec             Sometimes the term "baud" is						incorrectly used to refer to bits per second. Baud refers to symbols per second. Modern modems transmit several bits per symbol. byte                 8 bit               Not all machines had 8 bit B                    byte                  bytes, but these days most of them do. But beware: for transmission over modems, a						few extra bits are used so						there are actually 10 bits per byte. nybble               4 bits              Half of a byte. Sometimes equal to different lengths such as 3 bits. nibble               nybble meg                  megabyte            Some people consider these units along with the kilobyte gig                  gigabyte            to be defined according to					      powers of 2 with the kilobyte equal to 2^10 bytes, the megabyte equal to 2^20 bytes and the gigabyte equal to 2^30 bytes but these usages are forbidden by SI. Binary prefixes have been defined by IEC to replace the SI prefixes. Use them to					     get the binary values: KiB, MiB, and GiB. jiffy                0.01 sec    This is defined in the Jargon File jiffies              jiffy       (http://www.jargon.org) as being the duration of a clock tick for measuring wall-clock time. Supposedly the value used to be 1|60 sec or 1|50 sec depending on the frequency of AC power, but then 1|100 sec became more common. On linux systems, this term is used and for the Intel based chips, it does have the value of .01 sec. The Jargon File also lists two other definitions: millisecond, and the time taken for light to travel one foot.

Musical measures. Musical intervals expressed as ratios. Multiply two intervals together to get the sum of the interval. The function musicalcent can be used to convert ratios to cents.

Perfect intervals

octave               2 majorsecond          musicalfifth^2 / octave majorthird           5|4 minorthird           6|5 musicalfourth        4|3 musicalfifth         3|2 majorsixth           musicalfourth majorthird minorsixth           musicalfourth minorthird majorseventh         musicalfifth majorthird minorseventh         musicalfifth minorthird

pythagoreanthird     majorsecond musicalfifth^2 / octave syntoniccomma        pythagoreanthird / majorthird pythagoreancomma     musicalfifth^12 / octave^7

Equal tempered definitions

semitone             octave^(1|12) musicalcent (x) [1;1]   semitone^(x/100) ; 100 log(musicalcent)/log(semitone)

Musical note lengths.

wholenote            ! halfnote             1|2 wholenote quarternote          1|4 wholenote eighthnote           1|8 wholenote sixteenthnote        1|16 wholenote thirtysecondnote     1|32 wholenote sixtyfourthnote      1|64 wholenote dotted               3|2 doubledotted         7|4 breve                doublewholenote semibreve            wholenote minimnote            halfnote crochet              quarternote quaver               eighthnote semiquaver           sixteenthnote demisemiquaver       thirtysecondnote hemidemisemiquaver   sixtyfourthnote semidemisemiquaver   hemidemisemiquaver

yarn and cloth measures

yarn linear density

woolyarnrun          1600 yard/pound  1600 yds of "number 1 yarn" weighs a pound. yarncut              300 yard/pound  Less common system used in					 Pennsylvania for wool yarn cottonyarncount      840 yard/pound linenyarncount       300 yard/pound  Also used for hemp and ramie worstedyarncount     1680 ft/pound metricyarncount      meter/gram denier               1|9 tex           used for silk and rayon manchesteryarnnumber drams/1000 yards  old system used for silk pli                  lb/in typp                 1000 yd/lb asbestoscut          100 yd/lb   used for glass and asbestos yarn

tex                  gram / km   rational metric yarn measure, meant drex                 0.1 tex     to be used for any kind of yarn poumar               lb / 1e6 yard

yarn and cloth length

skeincotton          80*54 inch  80 turns of thread on a reel with a 				       54 in circumference (varies for other				       kinds of thread) cottonbolt           120 ft      cloth measurement woolbolt             210 ft

bolt                 cottonbolt heer                 600 yards cut                  300 yards   used for wet-spun linen yarn lea                  300 yards

drug dosage

mcg                  microgram       Frequently used for vitamins iudiptheria          62.8 microgram  IU is for international unit iupenicillin         0.6 microgram iuinsulin            41.67 microgram drop                 1|20 ml         The drop was an old "unit" that was replaced by the minim. But I was told by a pharmacist that in his profession, the conversion of 20 drops per ml is actually used. bloodunit            450 ml          For whole blood. For blood components, a blood unit is the quanity of the component found in a blood unit of whole blood. The human body contains about 12 blood units of whole blood.

fixup units for times when prefix handling doesn't do the job

hectare              hectoare megohm               megaohm kilohm               kiloohm microhm              microohm megalerg             megaerg   'L' added to make it pronounceable [18].

olddollargold        23.22 grains goldprice  Used until 1934 newdollargold        96|7 grains goldprice  After Jan 31, 1934 dollargold           newdollargold poundgold            113 grains goldprice

Nominal masses of US coins. Note that dimes, quarters and half dollars have weight proportional to value. Before 1965 it was $40 / kg.

USpennyweight        2.5 grams        Since 1982, 48 grains before USnickelweight       5 grams USdimeweight         10 cents / (20 US$ / lb)  Since 1965 USquarterweight      25 cents / (20 US$ / lb)  Since 1965 UShalfdollarweight   50 cents / (20 US$ / lb)  Since 1971 USdollarmass         8.1 grams

British currency

quid                 britainpound       Slang names fiver                5 quid tenner               10 quid

shilling             1|20 britainpound  Before decimalisation, there oldpence             1|12 shilling      were 20 shillings to a pound, farthing             1|4 oldpence       each of twelve old pence crown                5 shilling brpenny              0.01 britainpound pence                penny tuppence             2 pence tuppenny             tuppence oldpenny             oldpence oldtuppence          2 oldpence oldtuppenny          oldtuppence threepence           3 oldpence   threepence never refers to new money threepenny           threepence oldthreepence        threepence oldthreepenny        threepence oldhalfpenny         halfoldpenny oldhapenny           oldha'penny brpony               25 britainpound

Canadian currency

loony                1 canadadollar   This coin depicts a loon toony                2 canadadollar

Oceanographic flow

sverdrup             1e6 m^3 / sec  Used to express flow of ocean currents. Named after Norwegian oceanographer H. Sverdrup.

In vacuum science and some other applications, gas flow is measured as the product of volumetric flow and pressure. This is useful because it makes it easy to compare with the flow at standard pressure (one atmosphere). It also directly relates to the number of gas molecules per unit time, and hence to the mass flow if the molecular mass is known.

sccm                 atm cc/min    's' is for "standard" to indicate sccs                 atm cc/sec    flow at standard pressure scfh                 atm ft^3/hour scfm                 atm ft^3/min slpm                 atm liter/min slph                 atm liter/hour lusec                liter micron Hg / s  Used in vacuum science

Wire Gauge

This area is a nightmare with huge charts of wire gauge diameters that usually have no clear origin. There are at least 5 competing wire gauge systems to add to the confusion. The use of wire gauge is related to the manufacturing method: a metal rod is heated and drawn through a hole. The size change can't be too big. To get smaller wires, the process is repeated with a series of smaller holes. Generally larger gauges mean smaller wires. The gauges often have values such as "00" and "000" which are larger sizes than simply "0" gauge. In the tables that appear below, these gauges must be specified as negative numbers (e.g. "00" is -1, "000" is -2, etc). Alternatively, you can use the following units:

g00                   (-1) g000                  (-2) g0000                 (-3) g00000                (-4) g000000               (-5) g0000000              (-6)

American Wire Gauge (AWG) or Brown & Sharpe Gauge appears to be the most important gauge. ASTM B-258 specifies that this gauge is based on geometric interpolation between gauge 0000, which is 0.46 inches exactly, and gauge 36 which is 0.005 inches exactly. Therefore, the diameter in inches of a wire is given by the formula 1|200 92^((36-g)/39). Note that 92^(1/39) is close to 2^(1/6), so diameter is approximately halved for every 6 gauges. For the repeated zero values, use negative numbers in the formula. The same document also specifies rounding rules which seem to be ignored by makers of tables. Gauges up to 44 are to be specified with up to 4 significant figures, but no closer than 0.0001 inch. Gauges from 44 to 56 are to be rounded to the nearest 0.00001 inch.

In addition to being used to measure wire thickness, this gauge is used to measure the thickness of sheets of aluminum, copper, and most metals other than steel, iron and zinc.

wiregauge(g) [;m] 1|200 92^((36+(-g))/39) in;36+(-39)ln(200 wiregauge/in)/ln(92)

Next we have the SWG, the Imperial or British Standard Wire Gauge. This one is piecewise linear. It was used for aluminum sheets.

The following is from the Appendix to ASTM B 258

For example, in U.S. gage, the standard for sheet metal is based on the weight of the metal, not on the thickness. 16-gage is listed as   approximately .0625 inch thick and 40 ounces per square foot (the original    standard was based on wrought iron at .2778 pounds per cubic inch; steel    has almost entirely superseded wrought iron for sheet use, at .2833 pounds    per cubic inch). Smaller numbers refer to greater thickness. There is no   formula for converting gage to thickness or weight.

It's rather unclear from the passage above whether the plate gauge values are therefore wrong if steel is being used. Reference [15] states that steel is in fact measured using this gauge (under the name Manufacturers' Standard Gauge) with a density of 501.84 lb/ft3 = 0.2904 lb/in3 used for steel. But this doesn't seem to be the correct density of steel (.2833 lb/in3 is closer).

This gauge was established in 1893 for purposes of taxation.

Old plate gauge for iron

Manufacturers Standard Gage

A special gauge is used for zinc sheet metal. Notice that larger gauges indicate thicker sheets.

Screw sizes

In the USA, screw diameters are reported using a gauge number. Metric screws are reported as Mxx where xx is the diameter in mm.

Ring size. All ring sizes are given as the circumference of the ring.

USA ring sizes. Several slightly different definitions seem to be in circulation. According to [15], the interior diameter of size n ring in inches is 0.32 n + 0.458 for n ranging from 3 to 13.5 by steps of 0.5. The size 2 ring is inconsistently 0.538in and no 2.5 size is listed.

However, other sources list 0.455 + 0.0326 n and 0.4525 + 0.0324 n as the diameter and list no special case for size 2. (Or alternatively they are 1.43 + .102 n and 1.4216+.1018 n for measuring circumference in inches.) One reference claimed that the original system was that each size was 1|10 inch circumference, but that source doesn't have an explanation for the modern system which is somewhat different.

Old practice in the UK measured rings using the "Wheatsheaf gauge" with sizes specified alphabetically and based on the ring inside diameter in steps of 1|64 inch. This system was replaced in 1987 by British Standard 6820 which specifies sizes based on circumference. Each size is 1.25 mm different from the preceding size. The baseline is size C which is 40 mm circumference. The new sizes are close to the old ones. Sometimes it's necessary to go beyond size Z to Z+1, Z+2, etc.

Japanese sizes start with size 1 at a 13mm inside diameter and each size is 1|3 mm larger in diameter than the previous one. They are multiplied by pi to give circumference.

The European ring sizes are the length of the circumference in mm minus 40.

Abbreviations

mph                  mile/hr mpg                  mile/gal kph                  km/hr fL                   footlambert fpm                  ft/min fps                  ft/s rpm                  rev/min rps                  rev/sec mi                   mile mbh                  1e3 btu/hour mcm                  1e3 circularmil ipy                  inch/year   used for corrosion rates ccf                  100 ft^3    used for selling water [18] Mcf                  1000 ft^3   not million cubic feet [18] kp                   kilopond kpm                  kp meter kWh                  kW hour hph                  hp hour

Radioactivity units

becquerel            /s          Activity of radioactive source Bq                   becquerel curie                3.7e10 Bq   Defined in 1910 as the radioactivity Ci                   curie       emitted by the amount of radon that is in equilibrium with 1 gram of radium. rutherford           1e6 Bq

gray                 J/kg        Absorbed dose of radiation Gy                   gray rad                  1e-2 Gy     From Radiation Absorbed Dose rep                  8.38 mGy    Roentgen Equivalent Physical, the amount of radiation which, absorbed in the body, would liberate the same amount of energy as 1 roentgen of X rays would, or 97 ergs.

sievert              J/kg        Dose equivalent:  dosage that has the Sv                   sievert       same effect on human tissues as 200 rem                  1e-2 Sv       keV X-rays. Different types of					radiation are weighted by the Relative Biological Effectiveness (RBE).

Radiation type      RBE X-ray, gamma ray    1 beta rays, > 1 MeV  1 beta rays, < 1 MeV 1.08 neutrons, < 1 MeV  4-5 neutrons, 1-10 MeV  10 protons, 1 MeV     8.5 protons, .1 MeV     10 alpha, 5 MeV        15 alpha, 1 MeV        20

The energies are the kinetic energy of the particles. Slower particles interact more, so they are more effective ionizers, and hence have higher RBE values.

rem stands for Roentgen Equivalent Mammal

roentgen           2.58e-4 C / kg  Ionizing radiation that produces 1 statcoulomb of charge in 1 cc of dry air at stp. rontgen              roentgen    Sometimes it appears spelled this way sievertunit          8.38 rontgen  Unit of gamma ray dose delivered in one hour at a distance of 1 cm from a					point source of 1 mg of radium enclosed in platinum .5 mm thick.

eman                 1e-7 Ci/m^3  radioactive concentration mache                3.7e-7 Ci/m^3

A few German units as currently in use.

zentner              50 kg doppelzentner         2 zentner pfund                500 g

Some definitions using ISO 8859-1 characters

¢                    cent £                    britainpound ¥                    japanyen ångström             angstrom Å                    angstrom röntgen              roentgen

The following units were in the unix units database but do not appear in this file:

wey     used for cheese, salt and other goods. Measured mass or   waymass  volume depending on what was measured and where the measuring took place. A wey of cheese ranged from 200 to 324 pounds.

sack    No precise definition

spindle The length depends on the type of yarn

block   Defined variously on different computer systems

erlang  A unit of telephone traffic defined variously. Omitted because there are no other units for this dimension. Is this true? What about CCS = 1/36 erlang? Erlang is supposed to be dimensionless. One erlang means a single channel occupied for one hour.