This thread got polluted long ago. Simple method to do things. Want to do it different, have at it. @RustyRatRod
Much the same as the accuracy of the MSD bushings, one being .002 larger than another. You aren't going to get an engine timed to a level of precision using manual inputs where the margin for error exceeds your manufacturing tolerances. If you can pick up on .01 degree difference with a light.. you're darn good!