This is a special 10 cm ruler with holes. Holes improve the precision of the pencil sign preventing lines instead of dots. The bigger hole can hold the sharp cone piece so that the ruler becomes compasses.Use the inclined part to draw straight lines. Use the relief lines to measure (centimeters). Insert a sharp pencil in the dots to sign precise points. Insert the sharp cone in the biggest hole and a pencil in one of the remaining dots to use the ruler as compasses and draw circles from 2 to 20 centimeters in diameter.