# Deca-
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{{Short description|Numerical prefix meaning "ten"}}
{{Other uses|Deca (disambiguation){{!}}Deca}}
{{Wiktionary|deca-}}
{{Wiktionary|deca-|deka-|dec-}}
'''Deca''' (and '''dec'''; sometimes '''deka''') is a common [English-language](/source/English_language) [numeral prefix](/source/numeral_prefix) derived from the [Late Latin](/source/Late_Latin) {{Lang|la|decas}} ("(set of) ten"), from [Ancient Greek](/source/Ancient_Greek) {{Lang|grc|δεκάς (dekás)}}, from {{Lang|grc|δέκα}} (déka, "[ten](/source/10_(number))").[{{Cite book|title=Chambers Twentieth Century Dictionary|date=1979|page=332}}] It is used in many words.
It is also a [decimal](/source/decimal_prefix) [unit prefix](/source/unit_prefix) in the [International System of Units](/source/International_System_of_Units) (SI) denoting a factor of ten, with symbol '''da''' and spelled "deca" internationally{{efn|As used by the [International Bureau of Weights and Measures](/source/International_Bureau_of_Weights_and_Measures).[[https://www.bipm.org/en/publications/si-brochure/chapter3.html ''Decimal multiples and submultiples of SI units''] {{Webarchive|url=https://web.archive.org/web/20190330005801/https://www.bipm.org/en/publications/si-brochure/chapter3.html |date=2019-03-30 }}, 2006, SI Brochure: The International System of Units (SI), 8th edition]}} (or "deka" in [American spelling](/source/American_and_British_English_spelling_differences)[[http://physics.nist.gov/Pubs/SP811/sp811.html ''Guide for the Use of the International System of Units (SI)''], 1995, NIST Special Publication 811]).
==SI==
The prefix was a part of the original metric system in 1795. It is not in very common usage, although the deca[pascal](/source/pascal_(unit)) is occasionally used by [audiologist](/source/audiologist)s. The deca[newton](/source/newton_(unit)) is also encountered occasionally, probably because it is an SI approximation of the [kilogram-force](/source/kilogram-force).
Its use is more common in [Central Europe](/source/Central_Europe). In German, Polish, Czech, Slovak, and Hungarian, ''deka'' (or ''deko'') is common, and used in self-standing form, always meaning ''[decagram](/source/Kilogram)''.
A [runway](/source/runway) number typically indicates its [magnetic](/source/Compass) [azimuth](/source/azimuth) in [decadegree](/source/decadegree)s.
Before the symbol as an [SI prefix](/source/SI_prefix) was standardized as ''da'' with the introduction of the [International System of Units](/source/International_System_of_Units) in 1960, various other symbols were more common, such as ''dk'' (e.g., UK and Austria, still common in Hungary for decagrams), ''D'' (e.g., Germany, Eastern Europe), and ''Da''. For syntactical reasons, the [HP 48](/source/HP_48G), [49, 50](/source/HP_49%2F50_series) series, as well as the [HP 39gII](/source/HP_39gII) and [Prime](/source/HP_Prime) calculators use the unit prefix ''D''.[{{cite book | title=HP 48G Series – User's Guide (UG) | publisher=[Hewlett-Packard](/source/Hewlett-Packard) | edition=8 | date=December 1994 | id=HP 00048-90126, (00048-90104) | orig-year=1993 | url=http://www.hpcalc.org/details.php?id=3937 | access-date=2015-09-06}}][{{cite book | title=HP 50g graphing calculator user's guide (UG) | publisher=[Hewlett-Packard](/source/Hewlett-Packard) | edition=1 | date=2006-04-01 | id=HP F2229AA-90006 | url=http://www.hpcalc.org/details.php?id=6512 | access-date=2015-10-10}}][{{cite book | title=HP Prime Graphing Calculator User Guide (UG) | publisher=[Hewlett-Packard Development Company, L.P.](/source/Hewlett-Packard_Development_Company%2C_L.P.) | edition=1 | date=October 2014 | id=HP 788996-001 | url=http://h10032.www1.hp.com/ctg/Manual/c04119981.pdf | access-date=2015-10-13 | url-status=dead | archive-url=https://web.archive.org/web/20140903201341/http://h10032.www1.hp.com/ctg/Manual/c04119981.pdf | archive-date=2014-09-03 }}]
* 1 decametre = 10 [metre](/source/metre)s
* 1 decalitre = 10 [litre](/source/litre)s
* 1 [decare](/source/decare) = 10 [are](/source/Hectare)s
Examples:
* The [blue whale](/source/blue_whale) is approximately 30 metres, or 3 decametres, in length.[{{Cite web|url=http://channel.nationalgeographic.com/channel/content/kingdom-of-the-blue-whale-3302/blue-whale-facts/#/compare/length|archive-url=https://web.archive.org/web/20090306112952/http://channel.nationalgeographic.com/channel/content/kingdom-of-the-blue-whale-3302/blue-whale-facts/#/compare/length|url-status=dead|archive-date=March 6, 2009|title = National Geographic TV Shows, Specials & Documentaries}}]
==As an English prefix==
The prefix is used in many words.
===General===
* [Decathlon](/source/Decathlon), a combined event in athletics consisting of ten track and field events.
* [Decennial](/source/Decennial), ten-yearly or a celebration of ten years.
===Mathematics===
* [Decimal](/source/Decimal) based on the number ten.
* [Decagon](/source/Decagon) a plane figure with ten sides
* [Decahedron](/source/Decahedron) a polyhedron with ten faces
===Chemistry===
* [Decane](/source/Decane), a hydrocarbon with 10 carbon atoms
===Biology===
* [Decapoda](/source/Decapoda), an order of crustaceans with ten feet
===Religion===
* The [Decalogue](/source/Decalogue), the ''Ten Commandments''
==See also==
*[Metric prefix](/source/Metric_prefix)
==Notes==
{{notelist}}
==References==
{{reflist}}
== External links ==
{{Wiktionary|deca-}}
* [http://www.bipm.org BIPM website]
{{SI prefixes (infobox)}}
Category:SI prefixes
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Adapted from the Wikipedia article [Deca-](https://en.wikipedia.org/wiki/Deca-) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Deca-?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.