Tachometer

Here's a pleasingly old-school piece of cinema equipment for you. Since about 1930 (around the introduction of sound) films have generally been shot and projected at a standard 24 frames per second. Before that a variety of frame rates were used, often 16 or 18 fps, so when screening films from the silent era you ideally want a projector that can be adjusted to show the film at the proper rate (otherwise you get a jerky, speeded-up effect). Ours are adjustable (but of course!), and this is what is used to measure the speed of rotation of the reels and from that work out the fps, to check it's accurate.

I think I've got all that right, I may check with one of our lovely projectionists tomorrow to make sure. ;-)

I like the label in the lid of the box:
WARNING
When checking speeds in excess of 20,000 R.P.M. the tachometer must not be run longer than 10 seconds at a time. Allow bearing to cool before re-application.

Crikey!