"A/D scanning sequence appears to be as follows:
I think the time between samples was around 1 - 2 milliseconds. The anomaly I noticed was that for quadrant one [the lowest voltage level], I was reading about 50% more samples than any of the other three quadrants. I got a count of about 25,000 samples in quadrant one and about 15,000 samples in the other three quadrants. The number of transitions between each quadrant was around 2,000. I ran several experiments with similar results. [And I noticed about 0.1% transition errors]. I would have thought that all quadrants should have the same number of total samples read." Dick Swan
This can be explained partially by this photo: the blades
of the rotor are much larger than the space between them. Morover,
threshold of optical fork is probably asymmetrical, and go to
dark state as soon as light is partially blocked by blade, widening
it a bit more.