A variety of rulersA carpenter's ruleRetractable flexible rule ortape measureA closeup of a steel rulerA ruler in combination with a letter scale
Aruler, sometimes called arule, scale or aline gauge ormetre/meter stick, is an instrument used to makelength measurements, whereby a length is read from a series of markings called "rules" along an edge of the device.[1] Usually, the instrument is rigid and the edge itself is astraightedge ("ruled straightedge"), which additionally allows one to draw straighter lines.
Rulers have long been made from different materials and in multiple sizes. Historically, they were mainlywood butplastics have also been used. They can be created with length markings instead of beingscribed. 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. 12 in or 30 cm in length, although some can go up to 100cm, it is useful for a ruler to be kept on a desk to help in drawing. Shorter rulers are convenient for keeping in a pocket.[2] Longer rulers, e.g., 46 cm (18 in), are necessary in some cases. Rigid wooden or plasticyardsticks, 1 yard long, andmeter sticks, 1 meter long, are also used. Classically, longmeasuring rods were used for larger projects, now superseded by thetape measure,the surveyor's wheel or laserrangefinders.
In geometry, straight lines between points may be drawn using a straightedge (ruler without any markings on it). Furthermore, it is also used to draw accurate graphs and tables.
Aruler 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 ofangle trisection. However, if two marks be allowed on the ruler, the problem becomes solvable.
In thehistory of measurement many distance units have been used which were based on human body parts such as thecubit,hand andfoot and these units varied in length by era and location.[3] In the late 18th century themetric system came into use and has been adopted to varying degrees in almost all countries in the world.
Rulers made ofivory were in use by theIndus Valley civilization period prior to 1500 BC.[4] Excavations atLothal (2400 BC) have yielded one such ruler calibrated to about 1.6 millimetres (1⁄16 in).[4] Ian Whitelaw holds that theMohenjo-Daro ruler is divided into units corresponding to 33.5 millimetres (1.32 in) and these are marked out in decimal subdivisions with amazing accuracy, to within 0.13 millimetres (0.005 in). Ancient bricks found throughout the region have dimensions that correspond to these units.[5]
Anton Ullrich invented the folding ruler in 1851. Frank Hunt later made the flexible ruler in 1902.[6]
The equivalent of a ruler for drawing or reproducing a smooth curve, where it takes the form of a rigid template, is known as aFrench curve. A flexible device that can be bent to the desired shape is known as aflat spline, or (in its more modern incarnation) aflexible curve. Historically, a flexiblelead rule used bymasons that could be bent to the curves of amolding was known as alesbian rule.[7]
Ludwig Wittgenstein famously used rulers as an example in his discussion oflanguage games in thePhilosophical Investigations (1953). He pointed out that thestandard 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.
^Klein, Herbert A.The science of measurement: a historical survey. Reprint, unabridged, corr. republ. der Ausg. New York, Simon & Schuster, 1974. ed. New York, NY: Dover, 1988. Print.
.jpg)
