Heading indicator

Dip error causes the magnetic compass to read incorrectly whenever the aircraft is in a bank, or during acceleration or deceleration, making it difficult to use in any flight condition other than unaccelerated, perfectly straight and level.

The heading indicator is arranged such that the gyro axis is used to drive the display, which consists of a circular compass card calibrated in degrees.

To counter for the effect of Earth rate drift a latitude nut can be set (on the ground only) which induces a (hopefully equal and opposite) real wander in the gyroscope.

Another sort of apparent drift exists in the form of transport wander, caused by the aircraft movement and the convergence of the meridian lines towards the poles.

The flux gate continuously senses the Earth's magnetic field, and a servo mechanism constantly corrects the heading indicator.