When I was first on squadron the sprogs were the ones that got lumbered with doing adjustments on the standby compasses when it was needed. We had to take an instrument tech in the back seat, (CF-100), and taxi out, both engines running and radar and other electrical systems operating, align the aircraft on a compass rose painted on the ground then adjust the standby compass over cardinal points with a brass screwdriver. We had another tech on the ground giving us hand signals for adjustments based on data that he got from a hand compass.
Come to think of it that device would have worked to pass adjustment values to the cockpit rather than the hand signals we used.
Although I may be off the mark, I guess this was what came to mind when you gave the brass hint.