A compass and method of operation are disclosed for finding the heading of a vehicle. The heading is found using a compass having a rotor with a compass magnet thereon and means on the rotor defining a reference line in known relation with the polar axis of the magnet. The angular displacement of the...http://www.google.se/patents/US4862594?utm_source=gb-gplus-sharePatent US4862594 - Magnetic compass system for a vehicle
