I recall in The Amateur Photographers Handbook by Aaron Sussman was depicted a Haynes Shutter Checker, I believe it was called. It was supposedly a phonograph disc that is set in motion and shot on film. I would think the object was to measure the angle of the motion-blurred image and calculate the shutter speed. Of course, those books date back to heaven-knows-when, most likely to be run on the 78rpm record players of the day, which were likely not highly accurate. Today there are strobes and DC motors allowing you to get turntable speed dead-on the money. If you don't mind burning up a few rolls of film, I bet it is still and excellent way to check shutter speeds. But now you can get cheap USB testers off ebay, which work very well on speeds below 1/50, but not so well on faster speeds of leaf shutters. So you'd use the USB tester for slow, and switch over to the Haynes on the faster ones, using up less film. Of course where are you going to find an old Haynes checker?