Metric prefix
The first uses of prefixes in SI date back to the definition of kilogram after the French Revolution at the end of the 18th century.
Several more prefixes came into use, and were recognised by the 1947 IUPAC 14th International Conference of Chemistry[5] before being officially adopted for the first time in 1960.
However, with the lack of a "μ" key on most typewriters, as well as computer keyboards, various other abbreviations remained common, including "mc", "mic", and "u".
[c] Because ASCII, EBCDIC, and other common encodings lacked code-points for "μ", this tradition remained even as computers replaced typewriters.
The LaTeX typesetting system features an SIunitx package in which the units of measurement are spelled out, for example, \qty{3}{\tera\hertz} formats as "3 THz".
[14] The units kilogram, gram, milligram, microgram, and smaller are commonly used for measurement of mass.
[citation needed] The kilometre, metre, centimetre, millimetre, and smaller units are common.
[citation needed] Larger multiples of the second such as kiloseconds and megaseconds are occasionally encountered in scientific contexts, but are seldom used in common parlance.
Long time periods are then expressed by using metric prefixes with the annum, such as megaannum (Ma) or gigaannum (Ga).
[citation needed] The SI unit of angle is the radian, but degrees, as well as arc-minutes and arc-seconds, see some scientific use.
[citation needed] Common practice does not typically use the flexibility allowed by official policy in the case of the degree Celsius (°C).
[citation needed] In use the joule and kilojoule are common, with larger multiples seen in limited contexts.
Metric prefixes rarely appear with imperial or US units except in some special cases (e.g., microinch, kilofoot, kilopound).
In astronomy, geology, and palaeontology, the year, with symbol 'a' (from the Latin annus), is commonly used with metric prefixes: ka, Ma, and Ga.[18] Official policies about the use of SI prefixes with non-SI units vary slightly between the International Bureau of Weights and Measures (BIPM) and the American National Institute of Standards and Technology (NIST).
Other obsolete double prefixes included "decimilli-" (10−4), which was contracted to "dimi-"[25] and standardised in France up to 1961.
The financial and general news media mostly use m or M, b or B, and t or T as abbreviations for million, billion (109) and trillion (1012), respectively, for large quantities, typically currency[28] and population.
[29] The medical and automotive fields in the United States use the abbreviations cc or ccm for cubic centimetres.
For nearly a century[clarification needed], engineers used the abbreviation MCM to designate a "thousand circular mils" in specifying the cross-sectional area of large electrical cables.
