@kenshirriff So the syncro input is comping from the aircraft, gets converted to a mechanical position and then a servo loop makes sure the instruments position matches the one “requested” by the syncro. (Update: The transformer is even more mad than I thought, it computes the angle difference simply by rotating the output coil and the magnetic field does the rest)

Mad … (in a good way)

I guess the extra servo step is because using the syncro to drive the instrument directly would require too much force an mess up the signalling and potentially measurement?