Many people have thought of making clocks by taking a linear vernier and bending it into a circle. This is not an adequate solution, and here are the reasons why.
A circular vernier has a static disc and a rotor that look like this:
This is what happens when the rotor rotates. The first picture is the rotor on its own; the second picture is the rotor on top of the static disc.
The resultant pattern does indeed rotate 12 times as fast as the rotor, just as the minute hand of a clock or watch rotates 12 times as fast as the hour hand.
But the pattern is far from being a simple hand pointing in a specific direction. It is impossible to read it with any accuracy. For example, here are two snapshots, one taken at 20 past the hour and one at 25 past the hour:
Even accepting that the “hands” in this picture are white on a black background, it is impossible to work out where they are pointing.
The vernier principle is necessary for the construction of clock displays with a single moving part, but it is not sufficient. The resulting displays do not work.
Optical gearing adds advanced mathematics, optics, and accurate engineering to produce workable clock displays with only one moving part.