LiteYear, I agree with you. I saw "synchro" and my eyes just glazed over. Then all I saw were all the quadrant detections, and I didn't like that as a purist. I never registered that zekeman had a good small-angle solution.
Good catch!
thread240-291259 in 2011 never arrived at an elegant solution. I think this is such a solution, using two analog multiplies:
If C1, S1 are the cosine and sine outputs of potentiometer 1, and C2, S2 are from pot 2, then
C1 * S2 - S1 * C2 = sine of error angle.
Similarly,
S1 * S2 + C1 * C2 =...
