Ruler
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2008-06-25T17:56:40Z
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{{dablink|This article is about the drawing and measuring instrument. For the person who rules a country, see [[Monarch]] or [[Lists of incumbents]].}}
[[Image:Lineale.jpg|thumb|right|180px|A variety of rulers]]
[[Image:CarpentersRule.png|thumb|right|180px|A 2 metre carpenter's rule]]
[[Image:TapeMeasure.png|thumb|right|180px|Retractable flexible rule]]
[[image:Steel_ruler_closeup.jpg|thumb|180px|A closeup of a steel ruler]]
A '''ruler''', or '''rule''', is an [[Measuring instrument|instrument]] used in [[geometry]], [[technical drawing]] and engineering/building to measure distances and/or to rule straight lines. Strictly speaking, the ''ruler'' is essentially a [[straightedge]] used to '''rule''' lines and the calibrated instrument used for determining measurement is called a 'measure'. However, common usage is that a ruler is a calibrated straightedge that can be used for making measurements.
==Types==
A Rule has the measurements start from the end, whereas a ruler has a gap between the end and the measurements.
Rulers have long been made of wood in a wide range of sizes. [[Plastics]] have been used since they were invented; they can be moulded with length markings instead of being [[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. 12 inches or 30cm 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. Longer rulers, e.g., 18 inches (45cm) are necessary in some cases. Rigid wooden or plastic [[yardstick]]s, 1 yard long and metre sticks, 1 metre long, are also used.
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.
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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 2 [[metre]] carpenter's rule which folds down to a length of 24 [[centimetres]] to easily fit in a pocket, and a 5 metre long 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 centimetres. 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.
== Ruler applications in geometry==
{{main|Compass and straightedge}}
In geometry, a ruler usually refers to an unmarked ruler (a[[straightedge]]), only used for drawing straight lines between points, not measuring.
A [[compass and straightedge|ruler and compass construction]] refers to constructions using an unmarked ruler and a compass. It is possible to bisect and angle into 2 equal parts with ruler and compass. It can be proved, though, that it is impossible to divide an angle into 3 equal parts using only a compass and straightedge—the problem of [[angle trisection]]. However, should a single mark be allowed on the ruler, the problem becomes solvable.
==In heraldry==
*The ruler (calibrated, though numbers are not shown) appears as a [[charge (heraldry)|charge]] in [[heraldry]], notably in the arms of [[Odouze]].
*The [[Freemason]]s are identified by a [[compass]] and [[Square and compasses|square]] device, the latter another type of ruler. Together, the tools represent judgement and discernment.
==See also==
{{Wiktionary}}
{{commonscat|Length measuring devices}}
<div class= style="-moz-column-count:2; column-count:2;">
* [[Anton Ullrich]] (1825 -1895) [[Folding ruler]] inventor
* [[Golomb ruler]]
* [[Measuring rod]]
* [[Perfect ruler]]
* [[Rulering (punishment)]]
* Scale rulers: [[architect's scale]] and [[engineer's scale]].
* [[Slide rule]]
* [[Geometry template]]
* [[Dividing engine]]
* Erin Howell
* [[Online ruler]]
</div>
{{Metalworking - Measuring tools and gauges}}
[[Category: Dimensional instruments]]
[[Category: Metalworking measuring instruments]]
[[Category:Woodworking measuring instruments]]
[[Category:Stonemasonary tools]]
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