Editing Metric prefix (section)

=== <span class="anchor" id="dimi"></span><span class="anchor" id="Double prefix"></span> Double prefixes ===
Double prefixes have been used in the past, such as ''micromillimetres'' or ''millimicrons'' (now [[nanometre]]s), ''micromicrofarads'' (μμF; now [[picofarad]]s, pF), ''kilomegatonnes'' (now [[gigatonne]]s), ''hectokilometres'' (now 100&nbsp;[[kilometre]]s) and the derived adjective ''hectokilometric'' (typically used for qualifying the fuel consumption measures).<ref name="Rowlett_2008_Millimicro">{{Cite dictionary
| first = Russ
| last = Rowlett
| year = 2008
| orig-year = 2000
| title = millimicro-
| dictionary = How Many? A dictionary of units of measurement
| publisher = [[University of North Carolina at Chapel Hill]]
| access-date = 29 August 2016
| url = http://www.unc.edu/~rowlett/units/dictM.html
| url-status = live
| archive-url = https://web.archive.org/web/20160829225351/https://www.unc.edu/~rowlett/units/dictM.html
| archive-date = 29 August 2016
}}</ref> These are not compatible with the SI.

Other obsolete double prefixes included "decimilli-" ({{10^|−4}}), which was contracted to "dimi-"<ref>{{Cite book
| first = Maurice
| last = Danloux-Dumesnils
| date = 1969
| title = The Metric System: A critical study of its principles and practice
| publisher = The Athlone Press
| page = 34
| isbn = 9780485120134
| url = https://books.google.com/books?id=ElHAAAAAIAAJ
| access-date = 9 October 2015
}} (a translation of the French original {{lang|fr|Esprit et bon usage du système métrique}}, 1965 <!-- or ''Étude critique du système métrique'', 1962 -->)</ref> and standardised in France up to 1961.

There are no more letters of the Latin alphabet available for new prefixes (all the unused letters are already used for units). As such, Richard J.C. Brown (who proposed the prefixes adopted for {{10^|±27}} and {{10^|±30}}) has proposed a reintroduction of compound prefixes (e.g. ''kiloquetta-'' for {{10^|33}}) if a driver for prefixes at such scales ever materialises, with a restriction that the last prefix must always be ''quetta-'' or ''quecto-''. This usage has not been approved by the BIPM.<ref>{{Cite journal
| first = Richard J.C.
| last = Brown
| date = 27 April 2022
| title = Reply to "Facing a shortage of the Latin letters for the prospective new SI symbols: Alternative proposal for the new SI prefixes"
| journal = Accreditation and Quality Assurance
| volume = 27
| issue = 3
| pages = 143–144
| doi = 10.1007/s00769-022-01499-7
| s2cid = 248397680
}}</ref><ref>{{Cite journal
| last1 = Brown
| first1 = Richard J.C.
| year = 2019
| title = Considerations on compound SI prefixes
| journal = Measurement
| volume = 140
| pages = 237–239
| doi = 10.1016/j.measurement.2019.04.024
| bibcode = 2019Meas..140..237B
| s2cid = 146092009
}}</ref>