The protractor, an instrument used for laying off and measuring angles, is made of steel, brass, horn, or paper. When made of metal the central portion is cut out, Fig. 31, so that the draftsman may see the drawing. The outer edge is divided into degrees and tenths of degrees. To lay off the required angle - use a very sharp, hard pencil in order that the measurements may be accurate - place the protractor so that the two zero marks are on the given line, produced, if necessary, and the center of the circle is at the point through which the desired line is to be drawn.
Fig. 31. Protractor.