Optical Gearing is a method of getting a complete, readable clock display from just one moving part.
This looks like the hour hand and minute hand going round a clock. But there is no hour hand and no minute hand.
There is just a partly transparent disc like this:
revolving once every 12 hours, on top of a specially printed static disc like this:
And yet the viewer’s eye sees two independently moving objects, and it is easy to tell the time.
It is more than just two hands. Zooming in on one corner of the clock, one can see that there is even an indication of the seconds, rushing round the edge.
This is just one kind of Optical Gearing display. Many others are possible. Here are some examples:
Optical Gearing brings new purity to the display of time. It brings a sense of paradox as well, since one single moving thing generates so many different movements that are visible to the eye. No simulation on a screen can convey the strangeness of holding an Optical Gearing device in your hand, your eyes seeing something that your mind knows is impossible.
Optical Gearing works on a small scale, in watches, and on a large scale, in clocks.