Maltese Cross (Geneva Drive)

Maltese Cross (Geneva Drive) in detail

The story

The "Maltese cross" takes its name from the outline of its driven wheel, and its other name, "Geneva drive", from Swiss watchmakers, who used it to stop a mainspring from being overwound. In the 20th century it became the heart of the cinema projector: it is what moves the film forward frame by frame, then holds it perfectly still while the image is shown.

What you'll see move

Turn the drive wheel at a steady pace: the cross moves in jolts, a quarter turn at a time, then stops dead. You see the pin slide into a slot, push the cross round, slip out again, and the locking disc take over to hold it until the next pass.