The bevel protractor is used to establish and test angles to very close tolerances. It combined a compass with a protractor built into the base. The Irregular Polygon canvases and Protractor series further extended the concept of the shaped canvas. Finally, the initial angle could be measured with a simple protractor. The protractor on the upper left of the chart has two scales. The paired pedal protractor and retractor muscles operate the animal's foot. A dart was a "feather duster" and a protractor was mistaken for a "cockpit".