Goniometer

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.