Editing Unit of length (section)

===SI===
{{main article|International System of Units}}
{{See also|Orders of magnitude (length)}}
The [[SI base unit|base unit]] in the International System of Units (SI) is the [[meter]], defined as "the length of the path travelled by [[speed of light|light]] in vacuum during a time interval of {{frac|299792458}} seconds."<ref name="Res1">{{cite web |url=http://www.bipm.org/en/CGPM/db/17/1/ |title=17th General Conference on Weights and Measures (1983), Resolution 1. |access-date=2012-09-19}}</ref> It is approximately equal to {{val|1.0936|u=yards}}. Other SI units are derived from the meter by adding [[Metric prefix|prefixes]], as in millimeter or kilometer, thus producing systematic decimal multiples and submultiples of the base unit that span many orders of magnitude. For example, a [[kilometer]] is {{val|1000|u=meters}}.