### Types of angles

When we estimate and compare angles, we need to have something to compare them to. We begin with a revolution, and later we use a right angle as the angle of comparison.

#### Revolution

We start with a revolution, which is a full turn around the vertex and is equal to 360°.

#### Straight angle

A straight angle is half a revolution; the arms of the angle make a straight line. A straight angle measures 180°.