The scaling doesn't mean anything in reality. Its an exaggerated scale for 5 revolutions of a 3150hz test tone recorded from a test record. Each revolution is overlaid onto of each other, the smaller the circular plots the slow the deck is running, it can highlight some very interesting things about your deck. In the PFM thread somewhere there is a standard 1210 plot and it was not good, the deck or test record could have been at fault. Simons plot for his modified Kuzma was excellent.

This is one of my SP-10s before and after I matched the drive transistors after I took out one drive phase Hint: The green plot is the good one! Its also scaled to show the difference.