These 180 degree clear plastic protractors have both a 6 inch ruler edge and a 10 cm ruler on the open center. Pencil hole is located at the 3 inch ruler mark. The black markings clearly define the 1 degree increments making it easy to read. Plotting 0 to 180 degrees can be done left to right and right to left. Great for art or geometry class and home crafts. Pack of 10.