The measure of an angle is determined by the amount of rotation from the initial side to the terminal side. One way to measure an angle is in terms of **degrees**. A measure of one degree ($1\xb0$) is equivalent to a rotation of $\frac{1}{360}$ of a complete revolution.

To measure angles, it is convenient to mark degrees on the circumference of a circle. Thus, a complete revolution is $360\xb0$, half a revolution is $180\xb0$, a quarter of a revolution is $90\xb0$ and so forth.