Each rotation of OM corresponds to a certain angle.

# Zero angle of rotation

## If OM coincides with OK, then this arrangement of rays corresponds to the zero angle. In trigonometry, such a mutual arrangement of rays is called the initial position.

Zero angle of rotation

# Round angle of rotation

## This is a “full rotation” (rot) or “revolution” (rev) or “complete turn” or “full circle“.

If terminal side OM completes such a circle and afterwards coincides with OK, this is called a full circle (turn), which corresponds to an angle of 360° or 2π rad in the positive direction, and −360° (or −2π rad in the negative direction).

1 full circle = 1 rev = 1 turn = 1 rot = 360°

Positive full circle (Positive round angle). Revolution

# Right angle

If OM completes one fourth of a full circle, it results in a right angle (positive = 90° or negative = –90° depending on the direction of rotation).

Positive right angle

# Straight Angle (Flat angle)

If terminal side OM completes half a full circle, the result is a straight angle (or a flat angle).
If OM rotates counterclockwise, it forms a positive straight angle of 180°.
If OM rotates clockwise, it forms a negative straight angle of –180°.

Positive straight angle

# Inverse right angle

## If OM completes three fourths of a full circle (a three quarter rotation), it results in an inverse right angle (positive =270° or negative =–270° depending on the direction of rotation).

Positive three quarter rotation (Positive inverse right angle)