A goniometer is an instrument for angle measurement or drawing. It has a moving arm that can be rotated to a precise angular position.
The body the goniometer shown above has two protractors placed on it. The moving arm is attached to the center of the body by a fulcrum and rotates freely counterclockwise or clockwise around it.
You can think of the arms and center of the base of a goniometer as the components of an angle.
Follow these steps to measure an angle with a goniometer,
- Place the center point of the base over the angle's vertex.
- Place the stationary arm so its center line is over one side (the initial side) of the angle.
- Rotate the movable arm so its center line is over the other side (the terminal side) of the angle.
- The angle measure is the degree number on the protractor that the center line of the movable arm intersects.