Editing Ruler (section)

==History==
[[File:Nippur-Elle (Top).jpg|thumb|upright=1.5|The Nippur cubit-rod, {{circa|2650 BC}}, in the [[Istanbul Archaeology Museums|Archeological Museum]] of [[Istanbul]], Turkey]]
[[File:MaryRose-carpentry tools1.jpg|right|thumb|A wooden carpenter's rule and other tools found on board the 16th-century [[carrack]] ''[[Mary Rose]]'']]

In the [[history of measurement]] many distance units have been used which were based on human body parts such as the [[cubit]], [[Hand (unit)|hand]] and [[Foot (unit)|foot]] and these units varied in length by era and location.<ref>Klein, Herbert A. ''The science of measurement: a historical survey''. Reprint, unabridged, corr. republ. der Ausg. New York, Simon & Schuster, 1974. ed. New York, NY: Dover, 1988. Print.</ref> In the late 18th century the [[Metrication|metric system]] came into use and has been adopted to varying degrees in almost all countries in the world. 

The oldest preserved measuring rod is a copper-alloy bar that dates from {{circa}} 2650&nbsp;BC and was found by the German Assyriologist [[Eckhard Unger]] while excavating at the [[Sumer|Sumerian city]] of [[Nippur]] (present-day Iraq). 

Rulers made of [[ivory]] were in use by the [[Indus Valley civilization]] period prior to 1500&nbsp;BC.<ref name="Whitelaw14"/> Excavations at [[Lothal]] (2400&nbsp;BC) have yielded one such ruler calibrated to about {{convert|1/16|inch|mm|1|order=flip}}.<ref name="Whitelaw14">Whitelaw, p. 14.</ref> Ian Whitelaw holds that the [[Mohenjo-Daro]] ruler is divided into units corresponding to {{convert|1.32|inch|mm|1|order=flip}} and these are marked out in decimal subdivisions with amazing accuracy, to within {{convert|0.005|in|mm|order=flip}}. Ancient bricks found throughout the region have dimensions that correspond to these units.<ref>Whitelaw, p. 15.</ref>

[[Anton Ullrich]] invented the folding ruler in 1851. Frank Hunt later made the flexible ruler in 1902.<ref>{{cite web|title=Flexible Ruler Invented by Frank G. Hunt|url=http://americanhistory.si.edu/collections/search/object/nmah_1214954|website=National Museum of National History|access-date=7 June 2016|url-status=live|archive-url=https://web.archive.org/web/20160630014738/http://americanhistory.si.edu/collections/search/object/nmah_1214954|archive-date=30 June 2016}}</ref>