Plain English Meaning
A small cockpit unit that lets the pilot check and fine-tune whether the heading indicator is correctly lined up with magnetic north, and switch between automatic alignment and manual control.
Full Definition
A panel-mounted component of the remote indicating slaved gyro compass system that allows the pilot to monitor and adjust the alignment of the heading indicator with the magnetic flux detector (flux valve). It typically includes a slaving meter showing whether the gyro is properly aligned with magnetic north, a manual slaving switch to select free-gyro or slaved , and a compensator that corrects for small residual in the .