Editing Metric prefix (section)

=== Non-metric units ===
Metric prefixes are widely used outside the metric SI system. Common examples include the [[megabyte]] and the [[decibel]]. Metric prefixes rarely appear with [[imperial units|imperial]] or [[United States customary units|US]] units except in some special cases (e.g., microinch, kilofoot, [[kilopound]]). They are also used with other specialised units used in particular fields (e.g., [[megaelectronvolt]], [[gigaparsec]], [[millibarn]], [[kilodalton]]). In astronomy, geology, and palaeontology, the [[Year#Symbols|year]], with symbol 'a' (from the Latin ''annus''), is commonly used with metric prefixes: [[Kiloannus|ka]], Ma, and Ga.<ref>{{Cite encyclopedia
| last1 = Gargaud | first1 = Muriel
| last2 = Amils   | first2 = Ricardo
| last3 = Cleaves | first3 = Henderson James
| date = 2011-05-26
| df = dmy-all
| title = Ga
| encyclopedia = Encyclopedia of Astrobiology
| publisher = Springer Science & Business Media
| isbn = 978-3-642-11271-3
| lang = en
| page = 621
}}</ref>

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). For instance, the NIST advises that "to avoid confusion, prefix symbols (and prefix names) are not used with the time-related unit symbols (names) min (minute), h (hour), d (day); nor with the angle-related symbols (names) °&nbsp;(degree), ′&nbsp;(minute), and ″&nbsp;(second)",<ref name="Special Publication 811">{{Cite report
| last1 = Thompson | first1 = Ambler
| last2 = Taylor   | first2 = Barry N.
| date = March 2008
| title = Special Publication&nbsp;811
| edition = 2008
| publisher = [[National Institute of Standards and Technology]]
| url = http://physics.nist.gov/Pubs/SP811/sec06.html
| access-date = 21 June 2018
| via = nist.gov
| lang = en
}}</ref> whereas the BIPM adds information about the use of prefixes with the symbol ''as'' for arcsecond when they state: "However astronomers use milliarcsecond, which they denote mas, and microarcsecond, μas, which they use as units for measuring very small angles."<ref>{{Cite report
| title = The International System of Units (SI)
| series = SI Brochure
| publisher = International Bureau of Weights and Measures
| url = http://www.bipm.org/en/publications/si-brochure/chapter3.html
| access-date = 5 March 2017
}}</ref>