Ruler

From Free net encyclopedia

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.

Image:Lineale.jpg Image:CarpentersRule.png Image:TapeMeasure.png 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.

Several different designs of flexible instruments are 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. 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.

Practical rulers have distance markings along their edges. How these distance markings are applied and calibrated should be described here, including a history of old methods.

A ruler makes a popular tool for use as a pervertible, i.e. for corporal punishment, specifically called rulering, usually on the hands (either outstretched palms or knuckles) or thighs, and in BDSM. Generally, solid, heavy wooden or metal rulers are used for this purpose, but lighter, often flexible plastic ones can also be used punitively. Thus the wooden regla (Spanish for ruler) was widely used in schools to punish pupils: the 12" one was applied as a ferule (see palmeta) on the hands, the yard long one (made for drawing in the blackboard; rather like a yardstick) as a rod for spanking.

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

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Geometric constructions

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 unmarked ruler and a compass. It is known for instance, that the angle trisection problem is an impossible one, within the classic restriction of ruler bearing no marls. However, should a single mark be allowed on the ruler, the problem becomes solvable. It is common to call rulers in geometric context as straightedges.

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