The principle of applying controlled direct current to the flux valve to simulate rotation of the aircraft in a compass swing is discussed. The validity of the technique is demonstrated for the measurement of single cycle error and the MC-1 and MC-2 are shown as implementations of this technique. Work is now in process to eliminate calibration procedures, and to extend the technique to the pilot's standby compass and to aircraft with significant soft-iron error.

The precise navigation of modern aircraft requires an accurate source of heading information. In the primary mode of operation this signal is often obtained from an inertial reference, but the advent of inertial navigation has not eliminated the role of accurate magnetically slaved systems. A flux valve is often used to provide magnetic information to platform systems for use in initial alignment or in standby modes of operation and a magnetically slaved compass system, teamed with a doppler navigator, is still an excellent reference for long flights. For both applications full performance can only be obtained if the signal from the flux valve is carefully compensated in a compass swing.