Rotating the mirror in its mount through 22.5 degrees, gives a new radial upon which to perform 20 more foucult test from 1/4" to 5" out from the central axis along the focal plane.

When done, advance another 22 1/2 degrees, and repeat the proceedure. You can do this 15 times. before you are back to your starting radial.

Rather than using a protracter to measure the rotation of the mirror on its axis, a 31.42" X 1/4" paper strip is divided into 16 equal segments and glued to the mirror along its circumferance.

I used a thin piece of hook-up wire as a pointer, firmly attached to the ring clamp, in which the lens was rotated about its own axis.

I also constructed a table in which I recorded the results of each foucult test. Whenever the foucult test failed, I would determine if the actual focal point was ahead of or behind the desired focal plane. Thus in my table I would put a '+' a '-', or a '.' in the table for the test results.

I never had a single '-' in the table, and fortunately, most of the results were '.' signifying right on. The few '+'s I got were all on one of two radials that marked a single diagonal across the mirror.  This served to encourage me considerably, because all the '+'s fell so neatly onto a single diagonal. Of course I could identify the diagonal and apply longer polising strokes to its two radials.