They deliver a voltage level from hard over to the other way. The calibration process finds the center. So it is a linear voltage reading hard left to right depending. Not sure which way it is for that unit but a volt meter would tell you if it was working. It should be a stead increase to decrees as you back and forth. The computer would calibrate to the center point. Not uncommon for the sender to go bad, but the course computer could be bad too (worse).
s/v Bright Eyes Gozzard 36
37 15.7 N 76 28.9 W