Generally speaking,  a protractor is a circular or semicircular tool for measuring an angle or a circle. The units of measurement utilized are usually degrees.

          Some Rok protractors are simple half-discs; these have existed since ancient times. More advanced protractors, such as the Bevel Protractor have one or two swinging arms, which can be used to help measure the angle.

          External Protractors are instruments used on spheres to find a certain number of degrees