Ruler

A ruler, sometimes called a rule, scale, line gauge, or metre/meter stick, is an instrument used to make length measurements, whereby a length is read from a series of markings called "rules" along an edge of the device. 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.

Variants

Rulers have long been made from different materials and in multiple sizes. Historically, they were mainly wood but plastics have also been used. They can be created with length markings instead of being scribed. Metal is also 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. Typically in length, though some can go up to 100 cm, it is useful for a ruler to be on a desk or workstation to help in drawing. Shorter rulers are convenient for keeping in a pocket. Longer rulers (e.g. ) are necessary in some cases, some examples being the yardsticks and meter sticks. Historically, long measuring rods were used for larger projects, now superseded by the tape measure, the surveyor's wheel or laser rangefinders.

Use in geometry

In geometry, straight lines between points may be drawn using a straightedge (ruler without any rules on it). Furthermore, it is also used to draw accurate graphs and tables.

A ruler and compass construction is a construction that uses a ruler and a compass. It is possible to bisect an angle into two equal parts with a ruler and compass. It can be proven, 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, if two marks be allowed on the ruler, the problem becomes solvable via a neusis construction.

History

In the history of measurement many distance units have been used which were based on the human body such as the cubit, hand and foot, and these units varied in length by era and location. In the late 18th century, the metric system came into use and has since been adopted to varying degrees in almost all countries around the world.

The oldest preserved measuring rod is a copper-alloy bar that dates from 2650 BC and was found by the German Assyriologist Eckhard Unger while excavating at the Sumerian city of Nippur (present-day Iraq).

Rulers made of ivory were in use by the Indus Valley civilization period prior to 1500 BC. Excavations at Lothal (2400 BC) have yielded one such ruler calibrated to about .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.

Anton Ullrich invented the folding ruler in 1851. Frank Hunt later made the flexible ruler in 1902.

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 that 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.

Philosophy

Ludwig Wittgenstein famously used rulers as an example in his discussion of language games in the ''Philosophical Investigations'' (1953). 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. However, 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

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* Scales:
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References

Bibliography

* 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
* Russell, David R.; with photography by James Austin and foreword by David Linley (2010). '' Antique Woodworking Tools: Their Craftsmanship from the Earliest Times to the Twentieth Century'', Cambridge: John Adamson , pp. 64–74
* Whitelaw, Ian (2007). ''A Measure of All Things: The Story of Man and Measurement''. Macmillan

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Length, distance, or range measuring devices
Metalworking measuring instruments
Stationery
Stonemasonry tools
Woodworking measuring instruments
Mathematical tools