Clockwork Polarization Controller - Waveplate Calculator

Here's a clockwork model of a quater waveplate, and how it changes the polarization of light that's input to it.
https://en.wikipedia.org/wiki/Waveplate

The labels are the extreme points of the Poincare sphere, and are Horizontal, Vertical, Diagonal (+45deg), Antidiagonal (-45deg), Right-handed circular, and Left-handed circular.

You can actually use this to do complex calculations. More info here:
https://tinkeringsdotorg.wordpress.com/2018/08/31/clockwork-waveplates-polarization-calculations-with-gears/