Background: the vernier principle

On the face of a clock or a watch, hours and minutes move at different speeds. For one moving object to indicate them both, the indications have to move at a different speed from the indicator.

This sounds paradoxical, so here is an illustration of the basic principles.

A fixed base has a black and white pattern printed on it.

Vernier stator



A transparent slider has a black pattern printed on it.

Vernier rotor



Placing the slider on the base makes a larger pattern.

Vernier both



Moving the slider slowly…

Vernier moving rotor



… moves the larger pattern much faster when the slider is placed on the base.

Vernier moving both



In this case the pattern moves 12 times faster than the slider. In fact any ratio of speed is possible.

These phenomena are well known. Many people have thought that they could make clocks by using a circular vernier.

The Inadequacy of the Circular Vernier

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