Used to mean something else in the world of machinery and auto mechanics. Old school stuff. There is a screw that holds the distributor cap in place. A mechanic would loosen that screw and rotate the whole distributor cap very slightly, maybe 5° or so, the thing is round, so that’s a really small portion of a circle. So one could turn it clockwise or counterclockwise to advance or retard the timing.
That’s the nearest to him actually having a facial expression that I think I have ever seen