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{{short description|An instrument used to measure distances or to rule straight lines}}{{About|the measuring device|other uses}}{{Redirect|Carpenter's rule|the mathematical unfolding problem|Carpenter's rule problem}}(File:Lineale.jpg|thumb|right|upright=1.3|A variety of rulers)(File:CarpentersRule.png|thumb|right|A {{cvt|2|m|ftin|lk=on|frac=8}} carpenter's rule)File:TapeMeasure.png|thumb|right|Retractable flexible rule or tape measuretape measure(File:Steel ruler closeup.jpg|thumb|right|A closeup of a steel rule)A ruler, sometimes called a rule or line gauge, is a device used in geometry and technical drawing, as well as the engineering and construction industries, to measure or draw straight lines.WEB,weblink ruler noun - Definition, pictures, pronunciation and usage notes - Oxford Advanced Learner's Dictionary at,, 25 April 2018, no,weblink" title="">weblink 25 October 2017,


File:Gilded Bronze Ruler - 1 chi = 231 cm. Western Han (206 BCE - CE 8). Hanzhong City.jpg|thumb|left|Gilded bronze ruler. 1 chi = {{cvt|23.1|cm}}. Western Han (206 BCE – 8 CE). Hanzhong CityHanzhong CityFile:Bronze ruler. Han Dynasty 206 BCE to CE 220. Excavated in Zichang County..jpg|thumb|left|Bronze ruler. Han dynasty, 206 BCE – 220 CE. Excavated in 221x221pxRulers have long been made from different materials and in multiple sizes. Some are wooden. Plastics have also been used since they were invented; they can be molded with length markings instead of being (wikt:scribe|scribed). Metal is used for more durable rulers for use in the workshop; sometimes a metal edge is embedded into a wooden desk ruler to preserve the edge when used for straight-line cutting. {{cvt|12|in|cm|lk=on|disp=or}} in length is useful for a ruler to be kept on a desk to help in drawing. Shorter rulers are convenient for keeping in a pocket."Steel Rule Has Pocket Clip For Use As A Depth Gauge", Popular Science, December 1935, p. 887 bottom right. Longer rulers, e.g., {{cvt|18|in|cm}} are necessary in some cases. Rigid wooden or plastic yardsticks, 1 yard long, and meter sticks, 1 meter long, are also used. Classically, long measuring rods were used for larger projects, now superseded by tape measure, surveyor's wheel or laser rangefinders.Desk rulers are used for three main purposes: to measure, to aid in drawing straight lines and as a straight guide for cutting and scoring with a blade. Practical rulers have distance markings along their edges.A line gauge is a type of ruler used in the printing industry. These may be made from a variety of materials, typically metal or clear plastic. Units of measurement on a basic line gauge usually include inches, agate, picas, and points. More detailed line gauges may contain sample widths of lines, samples of common type in several point sizes, etc.Measuring instruments similar in function to rulers are made portable by folding (carpenter's folding rule) or retracting into a coil (metal tape measure) when not in use. When extended for use, they are straight, like a ruler. The illustrations on this page show a {{cvt|2|m|ftin}} carpenter's rule, which folds down to a length of {{cvt|25|cm|in|0}} to easily fit in a pocket, and a {{cvt|5|m|ft|0}} tape, which retracts into a small housing.A flexible length measuring instrument which is not necessarily straight in use is the tailor's fabric tape measure, a length of tape calibrated in inches and centimeters. It is used to measure around a solid body, e.g., a person's waist measurement, as well as linear measurement, e.g., inside leg. It is rolled up when not in use, taking up little space.A contraction rule is made having larger divisions than standard measures to allow for shrinkage of a metal casting. They may also be known as a shrinkage or shrink rule.Contraction rule {{webarchive|url= |date=2013-12-04 }}. Retrieved May 15, 2013.A ruler software program can be used to measure pixels on a computer screen or mobile phone. These programs are also known as screen rulers.

Ruler applications in geometry

In geometry, a ruler without any marks on it (a straightedge) may be used only for drawing straight lines between points. A straightedge is also used to help draw accurate graphs and tables.A ruler and compass construction refers to constructions using an unmarked ruler and a compass. It is possible to bisect an angle into two equal parts with ruler and compass. It can be proved, though, that it is impossible to divide an angle into three equal parts using only a compass and straightedge â€” the problem of angle trisection. However, should two marks be allowed on the ruler, the problem becomes solvable.


File:MaryRose-carpentry tools1.jpg|right|thumb|A wooden carpenter's rule and other tools found on board the 16th century carrack Mary RoseMary RoseIn the history of measurement many distance units have been used which were based on human body parts such as the cubit, hand and foot and these units varied in length by era and location.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. In the late 18th century the 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 BCE and was found by the German Assyriologist Eckhard Unger while excavating at Nippur. Rulers made of Ivory were in use by the Indus Valley Civilization period prior to 1500 BCE. Excavations at Lothal (2400 BCE) have yielded one such ruler calibrated to about {{convert|1/16|inch|mm|1}}.Whitelaw, p. 14. Ian Whitelaw holds that the Mohenjo-Daro ruler is divided into units corresponding to {{convert|1.32|inch|mm|1}} and these are marked out in decimal subdivisions with amazing accuracy, to within {{convert|0.005|in|mm}}. Ancient bricks found throughout the region have dimensions that correspond to these units.Whitelaw, p. 15.Anton Ullrich invented the folding ruler in 1851. Frank Hunt later made the flexible ruler in 1902.WEB, Flexible Ruler Invented by Frank G. Hunt,weblink National Museum of National History, 7 June 2016, no,weblink" title="">weblink 30 June 2016,

Curved and flexible rulers

The equivalent of a ruler for drawing or reproducing a smooth curve, where it takes the form of a rigid template, is known as a French curve. A flexible device which can be bent to the desired shape is known as a flat spline, or (in its more modern incarnation) a flexible curve. Historically, a flexible lead rule used by masons that could be bent to the curves of a molding was known as a lesbian rule.{{OED|lesbian, adj. and n. }} {{subscription}}


Ludwig Wittgenstein famously used rulers as an example in his discussion of language games in the Philosophical Investigations. He pointed out that the standard meter bar in Paris was the criterion against which all other rulers were determined to be one meter long, but that there was no analytical way to demonstrate that the standard meter bar itself was one meter long. It could only be asserted as one meter as part of a language game.

See also

{{div col|colwidth=30em}}
  • {{annotated link|Accuracy and precision}}
  • {{annotated link|Dividing engine}}
  • {{annotated link|Golomb ruler}}
  • {{annotated link|Measuring instrument}}
  • {{annotated link|Measuring rod}}
  • {{annotated link|Rolling ruler}}
  • Scales:
    • {{annotated link|architect's scale}}
    • {{annotated link|metric scale}} and
    • {{annotated link|engineer's scale}}
  • {{annotated link|Significant figures}}
  • {{annotated link|Technical drawing tool}}
{{div col end}}




  • Cherry, Dan. "Collector's guide to rules", Furniture & Cabinetmaking, no. 259, July 2017, ISSN 1365-4292, pp. 52–6
  • Rees, Jane and Mark (2010). The Rule Book: Measuring for the Trades. Lakeville, MN: Astragal Press {{ISBN|978-1-931626-26-2}} {{OCLC|907853704 }}
  • Russell, David R.; with photography by James Austin and foreword by David Linley (2010). (Antique Woodworking Tools|Antique Woodworking Tools: Their Craftsmanship from the Earliest Times to the Twentieth Century), Cambridge: John Adamson {{ISBN|978-1-898565-05-5}} {{OCLC|727125586}}, pp. 64–74
  • Whitelaw, Ian (2007). A Measure of All Things: The Story of Man and Measurement. Macmillan {{ISBN|0-312-37026-1}} {{OCLC|938084552}}
{{Wiktionary}}{{Commons category|Length measuring devices}}{{Measuring and alignment tools}}{{Metalworking navbox|toolopen}}

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