Editing Length (section)

== History ==
Measurement has been important ever since humans settled from nomadic lifestyles and started using building materials, occupying land and trading with neighbours. As trade between different places increased, the need for standard units of length increased. And later, as society has become more technologically oriented, much higher accuracy of measurement is required in an increasingly diverse set of fields, from micro-electronics to interplanetary ranging.<ref>History of Length Measurement, [http://resource.npl.co.uk/docs/educate_explore/posters/bg_historyoflength_poster.pdf  National Physical Laboratory] {{Webarchive|url=https://web.archive.org/web/20131126043209/http://resource.npl.co.uk/docs/educate_explore/posters/bg_historyoflength_poster.pdf |date=2013-11-26 }}</ref>

Under [[Albert Einstein|Einstein]]'s [[special relativity]], length can no longer be thought of as being constant in all [[reference frame]]s. Thus a [[Ruler (tool)|ruler]] that is one metre long in one frame of reference will not be one metre long in a reference frame that is moving relative to the first frame. This means the length of an object varies depending on the speed of the observer.