However, should two marks be allowed on the ruler, the problem becomes solvable. It can be proved, though, that it is impossible to divide an angle into three equal parts using only a compass and straightedge - the problem of angle trisection. It is possible to bisect an angle into two equal parts with a ruler and compass. A straightedge is also used to help draw accurate graphs and tables.Ī ruler and compass construction refers to constructions using an unmarked ruler and a compass. In geometry, a ruler without any marks on it (a straightedge) may be used only for drawing straight lines between points. It is used to measure the actual size of an object in Inches, Centimeters(CM), and millimeters (MM). These programs are also known as screen rulers or online ruler. It is rolled up when not in use, taking up little space.Ī Online ruler software program can be used to measure pixels on a computer screen or mobile phone. for a person's waist measurement, as well as for linear measurement, e.g., for the inside leg length. It is used to measure around a solid body, e.g. The illustrations on this page show a 2 m (6 ft 7 in) carpenter's rule, which folds down to a length of 25 cm (10 in) to easily fit in a pocket, and a 5 m (16 ft) tape, which retracts into a small housing.Ī flexible length-measuring instrument which is not necessarily straight in use is the tailor's fabric tape measure, a length of tape calibrated in inches and centimeters. When extended for use, they are straight, like a ruler. Measuring instruments similar in function to rulers are made portable by folding (carpenter's folding rule) or retracting into a coil (metal tape measure) when not in use. More detailed line gauges may contain sample widths of lines, samples of common type in several point sizes, etc. Units of measurement on a basic line gauge usually include inches, agate, picas, and points. These may be made from a variety of materials, typically metal or clear plastic. Practical rulers have distance markings along their edges.Ī line gauge is a type of ruler used in the printing industry. Classically, long measuring rods were used for larger projects, now superseded by tape measure, surveyor's wheel or laser rangefinders.ĭesk rulers are used for three main purposes: to measure, to aid in drawing straight lines, and as a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. Rigid wooden or plastic yardsticks, 1 yard long, and meter sticks, 1 meter long, are also used. Longer rulers, e.g., 18 in (46 cm), are necessary in some cases. Shorter rulers are convenient for keeping in a pocket. 12 in or 30 cm in length is useful for a ruler to be kept on a desk to help in drawing. 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. Historically they were mainly wooden but plastics have also been used since they were invented they can be molded with length markings instead of being scribed. Rulers have long been made from different materials and in multiple sizes. Since much technical work is now done on computer, many software programs implement virtual rulers to help the user estimate virtual distances. Rulers are ubiquitous in the engineering and construction industries, often in the form of a tape measure, and are used for making and reading technical drawings. At the high school level rulers are often used as straightedges for geometric constructions in Euclidean geometry. Children learn the basic use of rulers at the elementary school level, and they are often part of a student's school supplies. Their ability to quickly and easily measure lengths makes them important in the textile industry and in the retail trade, where lengths of string, fabric, and paper goods can be cut to size. They are important tools in the design and construction of buildings. They are commonly made from metal, wood, fabric, paper, and plastic. Rulers have been used since ancient times. Specialty rulers exist that have flexible edges that retain a chosen shape these find use in sewing, arts, and crafts. Some rulers, such as cloth or paper tape measures, are non-rigid. Commonly the instrument is rigid and the edge itself is a straightedge ("ruled straightedge") which additionally allows one to draw straight lines. A variety of rulers A 2 m (6 ft 6 + 3⁄ 4 in) carpenter's rule Retractable flexible rule or tape measure A closeup of a steel ruler A ruler in combination with a letter scaleĪ ruler, sometimes called a rule, line gauge, or scale, is an instrument used to make length measurements, whereby a user estimates a length by reading from a series of markings called "rules" along an edge of the device. For the mathematical unfolding problem, see Carpenter's rule problem.
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