Ruler

This article is about the drawing and measuring instrument. Ruler can also refer to a statesman in charge or ceremonial head of state of a country or minor politically significant principality; for this meaning see Monarch or Lists of incumbents.

A variety of rulers

A 2 metre carpenter\'s rule

Retractable flexible rule

A closeup of a steel ruler

A ruler or rule is an instrument used in geometry, technical drawing and engineering/building to measure distances and/or to rule straight lines. Strictly speaking, the ruler is the instrument used to rule lines and the calibrated instrument used for determining measurement is called a \'measure\'. However, common usage is that a ruler is calibrated so that it can measure.

Types

Several different designs of flexible instruments arnt used to determine length, such as the carpenter\'s rule, the ribbon-like tape measure used by tailors, and the retractable rule used especially in the construction trades and by home handyman, also known as a tape measure. As can be seen by the photos on this page, a 2 metre carpenter\'s rule can be folded down to a length of only 20 centimetres to easily fit in a pocket, and the 5 metre long tape easily retracts to fit within a small-sized housing.

Rulers can also be made out of steel. These serve three purposes: to measure, to aid in drawing straight lines and as a straight guide for cutting and scoring (with a knife or blade).

Practical rulers have distance markings along their edges.

• The ruler (calibrated, though numbers are not shown) appears as a charge in heraldry, notably in the arms of Odouze.

Ruler applications in geometry

Main article: Compass and straightedge

In geometry, a ruler usually refers to an unmarked ruler, only used for drawing straight lines between points, not measuring.

A ruler and compass construction thus refers to constructions using such an unmarked ruler and a compass. It is known, for instance, that the angle trisection problem is an impossible one if one follows the classical restriction to an unmarked ruler. However, should a single mark be allowed on the ruler, the problem becomes solvable. It is common to call such an unmarked ruler for use in geometric constructions a straightedge.

See also

Look up Ruler in
Wiktionary, the free dictionary.

Wikimedia Commons has media related to:

Length measuring devices

• 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
• Online ruler

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