"The box on the wall with all the coloured lights and switches is the changeover controller, used when one 2000ft (twenty minute) reel runs out and you start another. This is almost never done these days, with the film being made up onto large horizontal "cake stand" platters, but the circular dots in the top right of the screen are there to cue the changeover. The controller is much later than the projectors, and is a particularly nice addition, as on projectors that age you're normally down to flicking about eight switches in carefully-timed sequence to produce a seamless changeover. " - Phil