Servo control with Sine cosine potentiometers.

I have controller and motorized rotating device. The Controller is a knob the User can rotate. The rotating device is Propulsion Nozzle. Both the Controller and the Nozzle can be rotated over full 360 degrees – no limits. Both Controller and device are equipped with Sine Cosine Potentiometers.

I need the Nozzle to follow the Knob. In order to do that I need to compare output signals from the two sine cosine potentiometers and generate error signal. Error signal activate the motor and make the nozzle turn to follow the controller.

I am looking for simple (and preferably analog) way to compare outputs of the two Sine Cosine Potentiometers and generate error signal.

I expect there should be analog way to do it because the sine cosine pots were around before digital techniques came to being.