Protractor Protractor A protractor is a measuring instrument, typically made of transparent plastic or glass, for measuring angles. Most protractors measure angles in degrees (°). Radian-scale protractors measure angles in radians. Most protractors are divided into 180 equal parts. Some precision protractors further divide degrees into arcminutes. They are used for a variety of mechanical and engineering-related applications. One common use is in geometry lessons in schools. Some protractors are simple half-discs. More advanced protractors, such as the bevel protractor, have one or two swinging arms, which can be used to help measure the angle. A bevel protractor is a graduated
Scale of chords the centre point of this line. For a circle of radius , each half will be formula_1 so the chord will be formula_2. The line of chords scale represents each of these values linearly on a scale running from 0 to 60. It appears on Gunter's scale and the Foster Serle dialing scales. The commercial company Stanley marketed a metal version (Stanley 60R Line of Chords Rule) in 2015. Scale of chords A scale of chords may be used to set or read an angle in the absence of a protractor. To draw an angle, compasses describe an arc from