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Ruler

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	Topics Ruler Topic Home A ruler, or rule, is an instrumentMeasuring instrument Summary In physics and engineering, measurement is the activity of comparing physical quantities of real-world objects and events.... used in geometryGeometry Geometry arose as the field of knowledge dealing with spatial relationships.... , technical drawingTechnical drawing Technical drawing, also known as drafting or draughting, is the technique of creating accurate representations o... and engineering/building to measure distances and/or to rule straight lines. Strictly speaking, the ruler is essentially a straightedgeStraightedge A straightedge is a tool similar to a ruler, but without markings. ... used to rule lines and the calibrated instrument used for determining measurement is called a 'measure'. However, common usage is that a ruler is a calibrated straightedge that can be used for making measurements. Types A Rule has the measurements start from the end, whereas a ruler has a gap between the end and the measurements. Rulers have long been made of wood in a wide range of sizes. Plastics have been used since they were invented; they can be moulded with length markings instead of being scribed. Metal is 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 inches or 30cm in length is useful for a ruler to be kept on a desk to help in drawing. Shorter rulers are convenient for keeping in a pocket. Longer rulers, e.g., 18 inches (45cm) are necessary in some cases. Rigid wooden or plastic yardstickYardstick A yardstick is a tool used to physically measure lengths of up to three feet.... s, 1 yard long and metre sticks, 1 metre long, are also used. Desk rulers are used for three main purposes: to measure, to aid in drawing straight lines and as a straight guide for cutting and scoring with a blade. Practical rulers have distance markings along their edges. Measuring instruments similar in function to rulers are made portable by folding (carpenter's folding rule) or retracting into a coil (metal tape measureTape measure A tape measure or measuring tape is a ribbon of cloth, plastic, or metal with... ) when not in use. When extended for use they are straight, like a ruler. The illustrations on this page show a 2 metreMetre The metre, or meter , is a measure of length.... carpenter's rule which folds down to a length of 24 centimetres to easily fit in a pocket, and a 5 metre long tape which retracts into a small housing. A flexible length measuring instrument which is not necessarily straight in use is the tailor's fabric tape measureTape measure A tape measure or measuring tape is a ribbon of cloth, plastic, or metal with... , a length of tape calibrated in inches and centimetres. It is used to measure around a solid body, e.g., a person's waistWaist The waist is the part of the abdomen between the ribcage and hips.... measurement, as well as linear measurement, e.g., inside leg. It is rolled up when not in use, taking up little space. Ruler applications in geometry In geometry, a ruler usually refers to an unmarked ruler (a straightedgeStraightedge A straightedge is a tool similar to a ruler, but without markings. ... ), only used for drawing straight lines between points, not measuring. A ruler and compass constructionCompass and straightedge [Image:Pentagon construct.gif\|thumb\|right\|Construction of a regular pentagon]]... refers to constructions using an unmarked ruler and a compass. It is possible to bisect and angle into 2 equal parts with ruler and compass. It can be proved, though, that it is impossible to divide an angle into 3 equal parts using only a compass and straightedge—the problem of angle trisectionAngle trisection Overview The problem of trisecting the angle is a classic problem of compass and straightedge constructions of ancient Greek mathemat... . However, should a single mark be allowed on the ruler, the problem becomes solvable. In heraldry The ruler (calibrated, though numbers are not shown) appears as a chargeFacts About Charge (heraldry) In heraldry, a charge is an image occupying the field on an escutcheon.... in heraldryHeraldry Heraldry is the practice of designing, displaying, describing and recording coats of arms and badges, as well as the formal ... , notably in the arms of Odouze. The Freemasons are identified by a compassFacts About Compass A compass is a navigational instrument for finding directions on the earth.... and squareSquare and Compasses The Square and Compasses is the single most identifiable symbol of Freemasonry.... device, the latter another type of ruler. Together, the tools represent judgement and discernment. See also