When to Use Gyrocompass?

Gyrocompass, navigational instrument which makes use of a continuously driven gyroscope to accurately seek the direction of true (geographic) north. It operates by seeking an equilibrium direction under the combined effects of the force of gravity and the daily rotation of Earth.

What is the purpose of gyro error?

The error in the reading of the gyro compass, expressed in degrees east or west to indicate the direction in which the axis of the compass is offset from the north.

What is the difference between magnetic and gyro compass?

The gyrocompass

The direction a gyrocompass points is independent of the magnetic field of the Earth and depends upon the properties of the gyroscope and upon the rotation of the Earth. The axis of a free gyroscope will describe a circle around the pole of the heavens.