On Dec 17, 12:44*pm, Joseph Gwinn wrote:
...
So, I would command the spindle into a long series starts, stops,
reversals, and so on, that should leave the spindle in the same angular
position as before the sequence. *If no slippage, there will be little
or no difference between where the spindle ended up (as indicated with
the light beam) and the integral of the encoder output.

Joe Gwinn

Perhaps you could put the laser in the horizontal hole of a boring
head.

jsw