User:Daelin/Measurements Standard Proposal

Measurements
SI should be used wherever weights and measures are presented, followed parenthetically by any convenient conversion. When measurements or standards are recorded in non-SI units, indicate the source's units first, and SI parenthetically. If in doubt, favor SI first.

"Those conditions make Mount Waiʻaleʻale the wettest place on earth; it averages 11.7 m (460 in) of rain annually."

Writing SI units
Wikipedia takes a narrower approach than BIPM, who provides an English brochure as a guideline on SI. BIPM leaves details to groups like ISO, NIST, and IEEE. ISO 31 is especially relevant.

Roman (upright) type is used for units (and values), rather than italic. Unit and value are separated by a full space. Use &amp;nbsp; to prevent a line-break in the middle of a quantity. Unit symbols are unaltered in the plural ( cms, kgs, or mLs ), and are not followed by a full stop (period) except at the end of a sentence ( cm. kg. L. ).

Unit Algebra: Multiplied units are separated by a mid-high dot (&amp;middot;). Example: 98 N&middot;m Divided units are separated by a solidus (m/s), or carry a negative exponent (m&middot;s-1). The solidus is not followed by multiplied symbols unless ambiguity is avoided with parenthesis. "The permittivity of free space: 8.85 &times; 10-12 C2/(N&middot;m2)" Prefixes are inseparable from their unit symbol. "1 cm3 = (10-2 m)3 = 10-6 m3"</li></ul> </ol>

When written in paragraph, do not emphasise the quantity (value and unit) in any way. Unit names should never be mixed with unit symbols and mathematical notation. Spell out "meters per second", and not "meter/second". When the non-converted units are simple (meters, feet, newtons), they should usually be spelled out.

Choose units so that at most three or four digits are shown to the left of the decimal. For large areas, use m2, ha, and km2. For volumes, use m3, cm3, L, or mL. Do not use "cc" (1 cm3 = 1 mL), except by quotation, as it's a verbal shorthand.

Notes on specific units: For "degrees Celcius", use &amp;deg;C (eg, 27 &deg;C). The notation in 60&deg;47&prime;23&Prime; should only be used for arc length, and not for time or feet and inches. The symbols for durations of days, hours, minutes, and seconds are: d, h, min, s. The tonne, or metric ton, has the symbol and value of 1 t = 103 kg. Nautical miles and knots are acceptable for naval and aviation topics, but have no symbol. Millimeter of mercury (mmHg) and carat are non-SI source units for pressure and mass.

Non-SI units are problematic. Currently, no country on any continent prefers non-SI units (including the United States). Those countries which are not fully metricated, the United States and the United Kingdom, do not use systems which are compatible with each other. The US uses U.S. customary units, while the United Kingdom (in matters of drinking and driving) uses Imperial units. The UK has generally banned Imperial units in commerce, and the metric system is the preferred system of the United States. Both systems are defined in terms of SI units, and as such the SI system acts as a lingua franca.

It is polite to provide U.S. customary units or Imperial units in conversions, as appropriate to the article's topic.

Examples of when to prefer non-SI units
Road distances and speeds in the US and UK are labeled in miles. Sports such as American football are measured in yards. Newton stated his measurements in "Parisian pounds", so readers would know which definition of the pound he was using. US Letter paper is more accurately described as 8 1/2 in &times; 11 in than 216 mm &times; 279 mm. However, SI units should still be provided so non-US (and non-17th-century-Parisian) readers may relate to these values.

Binary unit prefixes
In computing, binary prefixes can be used to quantify large numbers where powers of two are more useful than powers of ten. They are commonly written and pronounced identically to the SI prefixes, but each successive prefix is multiplied by 1024 (210) rather than 1000 (103).

Using the prefixes kilo-, mega-, giga-, etc., and their symbols K, M, G, etc., in the binary sense can cause serious confusion. In January 1999, the International Electrotechnical Commission introduced in IEC 60027 the prefixes kibi-, mebi-, gibi-, etc., and the symbols Ki, Mi, Gi, etc. to specify binary multiples of a quantity. They have since been officially adopted by many other organizations.


 * Prefixes for binary multiples - NIST
 * When is a kilobyte a kibibyte? And an MB an MiB? - IEC

The use of the new binary prefix standards in the Wikipedia is not required, but is recommended for use in all articles where binary capacities are used. In articles where the precise byte capacities are important to description, the binary prefix should be used with binary capacities and the SI prefix should be used with decimal capacities (and should be noted as decimal if not immediately clear). If a contributor changes an article's usage from kilo- etc. to kibi- etc. where the units are in fact binary, that change should be accepted. However, because they are less familiar, binary unit prefixes such as MiB should be linked to avoid confusion. Link as MiB to avoid a disambiguation page.

Do not change all SI prefixes to IEC prefixes in computing contexts, only those that are actually being used in a binary sense. For example, do not change a "160 GB HDD" to "158.69 GiB" (still less "160 GiB"), but you can change 512 MB RAM to 512 MiB RAM where it is important to do so. (Notice that the number does not change because the SI prefix was used in a binary sense. Both usages are acceptable, but the MiB reference is less ambiguous.)

Measures that typically use decimal multiples:
 * Capacities of hard disk drives and some storage media
 * Network and bus speeds

Measures that typically use binary multiples:
 * Memory and cache sizes
 * Some storage media