In northern hemisphere, the plane azimuth is defined as the angle between south and collector plane. This angle is taken as negative toward east, i.e. goes in the antitrigonometric direction.

Example: south plane, azimuth = 0, east plane, azimuth = -90°.

In southern hemisphere, the plane azimuth is defined as the angle between north and collector plane. This angle is taken as negative toward east, i.e. goes in the trigonometric direction.