Safe-T 46110 mmArc Protractor Compass Plus, 15.8 cm Long, Made of Clear Plastic with Bluish Hue, Semicircular Side with Rotating Disc Inset on One Edge, Allows Direct View of Vertex Points Safe-T 46110 mmArc Protractor Compass Plus, 15.8 cm long, Made of Clear Plastic with Bluish Hue, Semicircular side with rotating disc inset on one edge, Spinning and Accurate Protractor revolves easily within a groove, Creates Circles from 10mm radius to 120mm radius on 1mm radius increments, Allows direct view of vertex points Straight Edge sides have inch/metric scales, Works well with Vis-a-Vis or other felt tip pens, Can be used with Rightstart Mathematics, Flat enough to use as a bookmark in a high school geometry or algebra text, Safe for Children, Dimensions 6.22 x 3.06 in x 0.06 in The disc has holes at distances of 10 to 19 mm from its center. The rectangular part of the instrument has ten rows of ten holes, at distances of 22 to 120 mm from the center of the disc. To draw circles, one fixes the disc at the center, places a pencil or other writing implement at the desired radius, and rotates either the disc or the rectangle The semicircular edge is divided to degrees and marked by 20s from zero to 180 in the clockwise direction and by 20s from 10 to 170 in the counterclockwise direction. The disc is marked: SAFE-T PROTRACTOR. It directs students to look at the upper, black numbers for angles facing left and at the lower, red numbers for angles facing right A scale of 11 centimeters, divided to millimeters, is along one edge, and a scale of four inches, divided to 16ths of an inch, is along the other edge.