Watch and clock glasses were originally made of glass, which often broke. After the advent of softer transparent material such as celluloid, and later, acrylics, replacement glasses could often be made by cutting them from a sheet of celluloid. This machine is designed to have a square of celluloid clamped against the flat side of its circular plate. This was turned by hand, and a pointed cutter, set to the right position for the required diameter was advanced towards the plate, cutting a perfectly circular disc, as in a lathe, ready to be fitted to the timepiece.