Photos of a pot from some piece of aircraft navigation equipment from the 1950's. Can't at the moment remember what it came from.
As you can see it is a pretty normal wirewound pot, until you look closer and realise the circle of screws is in fact a set of trimmers to slightly adjust the position of the wiper to correct for linearity errors in the resistence winding. The greased track has a follower which acts through 90 degrees to push the wiper mounting frame side to side. To those who have used a boring machine, it is a similar arrangement used to linearise the machine scales.
An impressive piece of engineering, wonder what it cost. Now replaced by an optical encoder and an EPROM. Such is progress.