Editing Deca-

{{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|English-language]] [[numeral prefix]] derived from the [[Late Latin]] {{Lang|la|decas}} ("(set of) ten"), from [[Ancient Greek]] {{Lang|grc|δεκάς (dekás)}}, from {{Lang|grc|δέκα}} (déka, "[[10 (number)|ten]]").<ref>{{Cite book|title=Chambers Twentieth Century Dictionary|date=1979|page=332}}</ref>  It is used in many words.

It is also a [[decimal prefix|decimal]] [[unit prefix]] in the [[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]].<ref name="bipm-spelling">[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</ref>}} (or "'''deka'''" in [[American and British English spelling differences#-re, -er|American spelling]]<ref name=SP811>[http://physics.nist.gov/Pubs/SP811/sp811.html ''Guide for the Use of the International System of Units (SI)''], 1995, NIST Special Publication 811</ref>).

==SI==
The prefix was a part of the original metric system in 1795. It is not in very common usage, although the deca[[pascal (unit)|pascal]] is occasionally used by [[audiologist]]s. The deca[[newton (unit)|newton]] is also encountered occasionally, probably because it is an SI approximation of the [[kilogram-force]]. 
Its use is more common in [[Central Europe]]. In German, Polish, Czech, Slovak, and Hungarian, ''deka'' (or ''deko'') is common, and used in self-standing form, always meaning ''[[Kilogram#SI_multiples|decagram]]''. 
A [[runway]] number typically indicates its [[Compass#How a magnetic compass works|magnetic]] [[azimuth]] in [[decadegree]]s.

Before the symbol as an [[SI prefix]] was standardized as ''da'' with the introduction of the [[International System of Units]] in 1960, various other symbols were more common, such as ''dk'' (e.g., UK and Austria), ''D'' (e.g., Germany, Eastern Europe), and ''Da''. For syntactical reasons, the [[HP 48G|HP 48]]<!-- at least 48G/GX/G+/GII, not sure about 48S/SX-->, [[HP 49/50 series|49, 50]] series, as well as the [[HP 39gII]] and [[HP Prime|Prime]] calculators use the unit prefix ''D''.<ref name="HP48_UG">{{cite book | title=HP&nbsp;48G Series – User's Guide (UG) | publisher=[[Hewlett-Packard]] | edition=8 | date=December 1994 | id=HP 00048-90126, (00048-90104) | orig-year=1993<!-- edition 1 (1993-05) --> | url=http://www.hpcalc.org/details.php?id=3937 | access-date=2015-09-06}}</ref><ref name="HP50g_UG">{{cite book | title=HP 50g graphing calculator user's guide (UG) | publisher=[[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}}</ref><ref name="HP-Prime_UG">{{cite book | title=HP Prime Graphing Calculator User Guide (UG) | publisher=[[Hewlett-Packard Development Company, 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 }}</ref>

* 1 decametre = 10 [[metre]]s
* 1 decalitre = 10 [[litre]]s
* 1 [[decare]] = 10 [[Hectare#Are|are]]s

Examples:
* The [[blue whale]] is approximately 30 metres or 3 decametres in length.<ref>{{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}}</ref>
{{SI prefixes (infobox)}}

==As an English prefix==
The prefix is used in many words.

===General===
* [[Decathlon]], a combined event in athletics consisting of ten track and field events.
* [[Decennial]], ten-yearly or a celebration of ten years.

===Mathematics===
* [[Decimal]] based on the number ten.
* [[Decagon]] a plane figure with ten sides
* [[Decahedron]] a  polyhedron with ten faces

===Chemistry===
* [[Decane]], a hydrocarbon with 10 carbon atoms

===Biology===
* [[Decapoda]], an order of crustaceans with ten feet

===Religion===
* The [[Decalogue]], the ''Ten Commandments''

==See also==
*[[Metric prefix]]

==Notes==
{{notelist}}

==References==
{{reflist}}

== External links ==
{{Wiktionary|deca-}}
* [http://www.bipm.org BIPM website]

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[[Category:SI prefixes]]