My neighbor at Houghton Lake was a test engineer for Oldsmobile. One of his jobs was to calibrate the instruments. Using a "fifth wheel" he would drive at a certain speed and then mark on a blank face plate where the indicator needle was at that speed. I have to say, some of the best (fastest) cars they made never saw the light of day. That could be a way to calibrate your tack if the face plate is not too hard to remove. . . 😆
