Registered Mechanic's Merc-o-Matic Diagnosis Guide

Another new wheel has made its way to us. It's an automotive illness diagnosis guide put out by the Ford Motor Company. It measures 5.75 inches across and is in reasonably good shape. I wonder if they still make these?

I can imagine a 1950s registered mechanic stepping aside to check his wheel. Maybe this would be good for the student as well. What I don't get is why the legend has A through K and then goes straight to W.  I would like to know what "excessive creeping" is.

This is yet another fine example of a wheel made by the talented folks at Perrygraf (still in the wheel business)! The copyright date is 1952.