Editing Deca- (section)

==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)}}