Editing Ruler (section)

{{Short description|Instrument used to measure distances}}
{{About|the measuring device-the ruler|other uses}}
{{Redirect|Carpenter's rule|the mathematical unfolding problem|Carpenter's rule problem}}
{{More citations needed|date=November 2023}}
[[File:Diverse·Maßstäbe,15.365.jpg|thumb|right|upright=1.3|A variety of rulers]]
[[File:CarpentersRule.png|thumb|right|A carpenter's rule]]
[[File:Measuring-tape.jpg|thumb|right|Retractable flexible rule or [[tape measure]]]]
[[File:Steel ruler closeup.jpg|thumb|right|A closeup of a steel ruler]]
[[File:Briefwaage Lineal.jpg|thumb|A ruler in combination with a letter scale]]

A '''ruler''', sometimes called a '''rule''', '''scale''', '''line gauge''', or '''metre/meter stick,''' is an instrument used to make [[length measurement]]s, whereby a length is read from a series of markings called "rules" along an edge of the device.<ref>{{cite web |title=ruler noun - Definition, pictures, pronunciation and usage notes - Oxford Advanced Learner's Dictionary at OxfordLearnersDictionaries.com |website=www.oxfordlearnersdictionaries.com |url=https://www.oxfordlearnersdictionaries.com/definition/english/ruler |access-date=25 April 2018 |url-status=live |archive-url=https://web.archive.org/web/20171025132533/http://www.oxfordlearnersdictionaries.com/definition/english/ruler |archive-date=25 October 2017}}</ref> Usually, the instrument is rigid and the edge itself is a [[straightedge]] ("ruled straightedge"), which additionally allows one to draw straighter lines. Rulers are an important tool  in geometry, geography and mathematics. They have been used since at least 2650 BC.