User:Gene Nygaard/sandbox/measurement

Units
The issue of whether all units should be metric (SI) is being debated at Measurements Debate, but they are always acceptable.


 * In scientific contexts, such as physics and chemistry, use SI units exclusively, but
 * if in a field a quantity is always given in one form, there is usually no need to perform a conversion. Link to the article explaining the unit, though. For example, atmospheric ozone concentration is measured in Dobson units.
 * The exact value and unit from the most reliable or, if applicable, normative source should always be retained, e.g. traffic speed limits in the UK and USA are in "mph", elsewhere "km/h", and "knots" in aquanautics, but nowhere "m/s". To avoid conversion edits that result in lesser accuracy, such instances should be made obvious.
 * Unless there is a historical or other reason to use one style over another, editors may choose whether to use metric, U.S. customary units, or Imperial units primarily. It may be helpful to readers to offer equivalents, but this should not be done if it reduces the flow of a sentence or otherwise interferes with the quality of the writing.
 * If equivalents are given, these should be to the same level of precision as the original measurement and in parentheses, for example, "the Moon is 400,000 km (250,000 miles) from Earth", not "(248,548.477 miles)".
 * Metric equivalents should be given for historical or unusual units, where these are appropriate. Multiple equivalents, i.e. metric and U.S. or imperial, are cumbersome and shall be avoided.

In-text written-out units are preferred ("two metres" instead of "2 m"); otherwise use standard abbreviations or symbols for metric units&mdash;m for metre, kg for kilogram, etc. (see SI for the list)&mdash;and two-letter abbreviations for inch-pound units&mdash;in for inch (not " or &Prime;), ft for foot (not ' or &prime;), yd for yard, mi for mile, lb for pound, gal for gallon, pt for pint, qt for quart, and so forth. Never append a plural s to abbreviations (no "kgs", "yds", "kts", or "lbs"). Where possible, use the symbols with unit combinations, for example use ft/s rather than fps.

The terms fluid ounce, pint, quart, gallon, barrel, and ton are ambiguous units, so they must be specified more precisely. You may assume that ounces and pounds are Avoirdupois unless otherwise indicated. When the unit is part of a quote, and is within quotation marks, it should not be changed, though a conversion may be added in brackets after the quote, if it is an unusual unit.

Areas of land should be given in square kilometres, km², which can be entered as km&amp;sup2;. This form is preferable to  km2 , which can add extra leading. When describing areas of agriculture, forests, parks, wilderness, etc., hectares (ha) are an acceptable (not mandatory) alternative to square kilometres. Smaller areas use m² etc.

Volumes should be given in cubic metres (m³) or litres (l or L), where it is common usage.

Note that the compact superscript style works well with areas and volumes (i.e. ² and ³), but where zero, four to nine or minus are required, one should resort to.

Larger masses may be given in tons (t) and for approximations it is often not necessary to disambiguate between the metric ton (sometimes "tonne") and the English tons, because they are quite similar in size.

In general, all SI prefixes are acceptable, but an editor may choose to use a subset thereof.

The reader should see a space between the value and the unit symbol: "25 kg", not "25kg". To ensure that the value and the unit symbol are displayed on the same line, editors should use a non-breaking space character rather than a standard space: type 25&amp;nbsp;kg rather than 25 kg. Avoid entering the character directly, even when possible, for some browsers substitute all instances of it with the normal, breaking space.

Measurements (both number and unit together) of dimensions with existing orders of magnitude pages should be linked to the appropriate page.

Examples

 * The highest score recorded for the Deuces High pinball game was 11,933,750.
 * The hippopotamus stands 1.5 m (5 ft) at the shoulders and weighs between 2,700 and 4,500 kg (6,000–9,900 lb).
 *  The hippopotamus stands 1.5&amp;nbsp;m (5&amp;nbsp;ft) at the shoulders and weighs between 2,700 and 4,500&amp;nbsp;kg (6,000&amp;ndash;9,900&amp;nbsp;lb). 
 * … between 2.7 and 4.5 tons.
 * The first sub-four-minute mile was run by Roger Bannister.
 * The 155 mm diameter projectile offers a wide range of options for battlefield usage.
 * 10² = 100
 *  10&amp;sup2; = 100 
 * A large number such as 156,234,000,000,000,000,000,000,000,000 can be concisely recorded as 1.56234×1029, and a small number such as 0.0000000000234 can be written as 2.34×10−11.
 *  A large number such as 156,234,000,000,000,000,000,000,000,000 can be concisely recorded as 1.56234&amp;times;1029, and a small number such as 0.0000000000234 can be written as 2.34&amp;times;10&amp;minus;11. 
 * The computer has a 160 GB HDD and 512 MiB of RAM.

See orders of magnitude and the talk page there for ongoing, possibly resolved debate on which style of exponent notation to use for large numbers.