[Radio Wrangler]

If it's the rotor I think it is, inside the controller, the motor drives the pointer via a gear train and it also drives a duplicate of the pot in the gear train inside the bell of the rotor proper up the tower.

This pot does just as much rotating as the main one, but it's in a nicer environment.

There is a possibility of wear in the gearing causing teeth to jump and a relative error builds up.

The motors can just rotate indefinitely. The alignments which are important are the bell position (meaning its stops) with respect to the pot position, and the pointer position (meaning its stops) with respect to its pot position.

The pointer can be loosened and moved, also the stub mast can be loosened and rotated. People do this so that they can place the stops position, that can't be rotated through, at a convenient compass heading they rarely use.

David