A goniometer measures range of motion in degrees. Physical therapists use goniometers to measure and track the range of motion of a joint such as an elbow, shoulder or knee throughout treatment. A goniometer works like a large compass; the centre section is marked with degrees, from zero to 360. It has two arms that extend from the circle, only one of which can move freely. The arm that does not move is mounted at zero degrees.
Trace the shape of the protractor onto one of the yardsticks. One curved side should but up against the end of the yardstick. The flat crossbar and the other curved side should mount flush with the yardstick and overlap the yardstick under the numbers 1 through 4. The other curved side should overlap at approximately number 5.
Cut away part of one of the yardsticks so that the protractor fits on top of the end of the yardstick.
Drill a hole through both yardsticks where the centre of the protractor should be.
Bolt the two yardsticks and the protractor together. Place washers between the protractor and the top yardstick. The finished goniometer should look like a compass.
Measure an angle by using the yardsticks to parallel the body parts being measured and read the angle on the protractor.