[ALIBI]

As a former gauge engineer.... why don't they come up with a simple set of GO/NO GO gauges? The GO would tell you if the trackball is too big in diameter and the NO GO would tell you if the trackball is too small in diameter. By passing through the GO, you would know the trackball was not too big and by not passing through the NO GO, you would know that the trackball was not too small. The gauges could be as simple as two pieces of lexan, if you wanted a 40" diameter trackball, one would have a 41" hole (GO, not larger than 41") and one would have a 39" hole (NO GO, not smaller than 39").

If you are more concerned with bounce/air pressure, a simple pressure gauge would work.