What is a Magnetic Compass, its principle, types and errors?

1. Freedom of movement of the gimbal.
2. Card floating freely and level, and rotating without any friction.
3. Liquid free of bubbles and clear.
4. Compass card clear and sharp (able to be read) with no distortion or discoloration.
5. Optical system (if any) correctly adjusted and clean.
6. Azimuth reading devices and means of illumination in working order.
7. No liquid leaks around seals or filler plugs.

 The compass deviation records and the deviation card for each magnetic compass installed on the ship should be checked. 

 What are Effects of Changes in Magnetism During the Life of a Ship?

Because the magnetism of a new ship can be particularly unstable, the performance of magnetic compasses should be monitored carefully during the early life of a ship, and adjustments made if necessary. Masters are advised that it is essential to check the performance of magnetic compasses particularly after: