• Catalan: regla
• Chinese: 尺 (chǐ), 直尺 (zhí chǐ)
• Croatian: ravnalo
• Czech: pravítko
• Dutch: meetlat
• Finnish: viivoitin
• French: règle
• German: Lineal
• Greek: κανών, χάρακας, υποδεκάμετρο, ρίγα
• Hebrew: סרגל
• Italian: righello
• Japanese: 定規 (じょうぎ, jōgi)
• Maltese: riga
• Polish: linijka
• Portuguese: régua
• Russian: линейка
• Serbian: crtalo , ravnalo
• Spanish: regla
• Swedish: linjal

• Catalan: líder, governant
• Croatian: vođa
• Czech: vládce
• Finnish: hallitsija
• German: Herrscher
• Greek: άρχοντας , αρχόντισσα , κυβερνήτης
• Hebrew: מנהיג ,שליט
• Hungarian: uralkodó
• Nahuatl: tecutli
• Portuguese: governante
• Russian: вождь (vožd’)
• Spanish: gobernante
• Swedish: härskare , ledare

''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 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 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 24 centimetres to easily fit in a pocket, and the 5 metre long tape easily retracts to fit within a small-sized housing.

Traditional construction for rulers has been of wood, with typical lengths for desk-sized rulers being 12 inches or 30cm in length, with 18 inch (45cm rulers) being less common. Yardsticks 36 inches (or 1 yard) in length were commonly also sold, also made of wood (in metric countries, these were 1 metre in length).

Desk-sized rulers came to serve three main purposes in common usage: to measure, to aid in drawing straight lines and as a straight guide for cutting and scoring (with a knife or blade). To facilitate the latter two, during the 20th century some manufacturers embedded metal straight-edges into the wood on one of the long sides, as wood was prone to chipping. Later in the century, rulers also came to be made out of steel, also in 12-inch (30cm) and 18-inch (45cm) lengths. Steel rulers were usually backed with a thin panel of cork affixed with adhesive, to prevent the ruler from sliding on a paper surface.

Practical rulers have distance markings along their edges.

Ruler applications in geometry

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.

In heraldry

• The ruler (calibrated, though numbers are not shown) appears as a charge in heraldry, notably in the arms of Odouze.
• The Freemasons are identified by a compass and square device, the latter another type of ruler. Together, the tools represent judgement and discernment.

See also

• 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

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