When we got our boat it had an ST1000 installed. It worked neat, however the heading in the window was about 70 degrees off the ship compass
Each time we went to calibrate it something interfered. One time we broke an impeller and had to abort, on time the power died and we had to rewire the supply power.
When it was working it always tracked and held the course once you hit auto however on a 270 course the window might be reading 345. I always had a sneaking suspicion that there was something wrong with the unit because the book calibration read like we would be taking out a minor error which I surmised to be 5-8 degrees, not 70+
Anyway, finally got my act together and took out 73 degrees of error and now Otto has had a brain transplant and agrees with the ship.