agroves -- Please note that I didn't say you couldn't feel a 1/16 difference, but that I didn't believe it would make your wrist sore. And I'll stick with that.
Regarding the Jonell vs plastic span guages, do I understand you to be saying that the Jonell is correct and the plastic is off? I use a plastic guage, but I also measure the span from my measuring ball with the same guage. Then I check the spans on my press (an old AMF 3600, a sidewinder) with the same guage, so the span I drill is the same as I measured, even if both are off 1/16. And the same comparison is true if I duplicate a layout from an existing ball. An error in the fit would occur only if someone told me to drill (for example) a 4 11/16 span and I measured it with a guage that was incorrect. -- JohnP