The compass is a separate tool that can also be used to measure angles and lengths. A compass can be opened wide, but has no measurements on it. Geometric compasses are drawing instruments used for drawing circles and arcs. The compass has two legs, one with a point and the other with a pencil or lead. The point can be placed in the center of the circle and the pencil can be adjusted to draw the proper sized circle. You can adjust the distance between the point and the pencil to adjust the size of the circle.