A goniometer is a device used for angle measurements. Its purpose is similar to that of a protractor, but the shape and method of use for a goniometer is different. The goniometer has at least one extra "arm," or lever, which can be rotated to help determine angle of position. Goniometers are used in a variety of industries, including architecture, geology and even the medical field -- they help physical therapists determine the range of movement in a person's joints. A simple goniometer can be built at home using a protractor and yard sticks.
Align the center of the circular protractor, which should have a middle bar running through it with one ruler. The ruler and middle bar should be on top of one another.
Place the second ruler on the opposite side of the protractor, also in line with the middle bar. The two rulers should be separated by the protractor, and the rulers should be parallel.
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Drill a hole through the two rulers and protractor right in the middle of the protractor circle.
Screw the bolt in through the hole and secure it with the bolt on the opposite side. Do not screw in the bolt too tightly, or else the two arms, which are the rulers, will not be able to move. For the goniometer to be useful, the levers need to be able to be moved.
Measure the angles of objects or drawings by placing the screw directly over the angle to be measured, and move the rulers to fit the angle. For example, if you wanted to measure the angle of a bent knee, place the screw over the knee, and adjust the arms to the position of the thigh and lower leg. Read the angle on the protractor.
Yard sticks can be used instead of rulers for large objects which need to be measured.