Having had problems recently the Raymarine
Rudder indicator is basically a potentiometer. Like the volume control on a radio
. At hard over it is low volume and all the other way it is loud. They calibrate the readout to be mid volume to indicate dead center. As the rudder post turns it adjusts the volume. Pretty simple but effective. The display is just a voltage reading.
I had a problem with mine and we proved the voltage coming back varied as expected and found the computer reading the voltage had the problem. Multiply the repair cost by 8.