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Learn more about "Ruler"
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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 implies that a ruler is a straightedge that is calibrated 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 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. 12 inches or 30 centimeter|cm 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 (45 cm) are necessary in some cases. Rigid wooden or plastic yardsticks, 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.
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-meter carpenter's rule which folds down to a length of 24 cm to easily fit in a pocket, and a 5-meter-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
In geometry, a ruler without any marks on it (a straightedge) may be used only 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 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 — the problem of angle trisection. However, should a single mark be allowed on the ruler, the problem becomes solvable.
History
[[File:MaryRose-carpentry tools1.jpg|right|thumb|A wooden carpenter's rule and other tools found on board the 16th century carrack ''Mary Rose''.]]
Rulers made from Ivory were in use by the Indus Valley Civilization period prior to 1500 BC.[Whitelaw, p. 14.] Ian Whitelaw holds that the Mohenjo-Daro ruler is divided into units corresponding to and these are marked out in decimal subdivisions with amazing accuracy, to within . Ancient bricks found throughout the region have dimensions that correspond to these units.[Whitelaw, p. 15.]
Anton Ullrich invented the folding ruler in 1851.
See also
- Dividing engine
- Geometry template
- Golomb ruler
- Measuring rod
- Rolling ruler
- Scale rulers: architect's scale and engineer's scale
References
Notes
Bibliography
- Whitelaw, Ian (2007). ''A Measure of All Things: The Story of Man and Measurement''. Macmillan. ISBN 0312370261.
External links
Category:Dimensional instruments
Category:Metalworking measuring instruments
Category:Stonemasonry tools
Category:Woodworking measuring instruments
Category:Stationery
simple:Ruler
zh-yue:間尺
Related Images- A variety of rulers
- A 2 metre carpenter's rule
- A closeup of a steel rule
Sources: StartLearningNow, Wikipedia | Usage license: GNU FDL
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