Got a new Vario today, and set forth to calibrate it. An initial test showed it wasn't very close, so I turned the adjustment tool a few turns "finer." Still not close, so I turned some more . No luck. Worse, the adjustment screw at some point seemed to start turning very freely, with no effect whatsoever. I feared I had unscrewed it or something. So I took the top burr out, then the bottom burr, then removed the faceplate, then removed the case, then removed the chute--and I still couldn't see how to access the adjustment screw. So I put it all back together, and noticed I couldn't move the macro lever all the way up without the motor laboring--the grinder was adjusted way too fine. After tearing out some hair, I looked closely at the adjustment tool--and noticed that the tip was more or less round, not hexagonal: I had stripped it. A quick trip to the belt grinder to shorten the tool a couple mm and I had a working adjustment tool. A few turns in the coarse direction and everything was perfect.
Lesson learned: sometimes you strip the screw, and sometimes you strip the tool.