Abstract: An electronic compass system for determining the heading of an armored vehicle containing a large mass of ferromagnetic material, which system comprises a plurality of sensors, and for real-time computation of the corrections required of actual magnetometer measurements. Part of the values used for the computation are computed in advance, and part in real-time. Some of the computations are based on the perturbation of the earth magnetic field based on an algorithm which takes into account one or two rotational prolate ferromagnetic ellipsoids which have certain dimensions and which are at a predetermined distance from each other either represent the body of an armored vehicle, or when two ellipsoids are used, they represent the hull and turret of a tank.