Apologies in advance for the question, but it's bothering me and may throw off my results slightly, so before I start measuring everything I currently have, I need to ask...

How do I measure for center of grip? If I draw a line straight between bottom of fingers and draw the center line perpendicular to that, it falls off towards the left side of my thumb. If I draw a line from center of thumb up thru fingers, the line will not be centered between the fingers. The lines are slightly off from each other, which will affect the measurements.

Which is correct?

Thanks in advance

Agreed and thanks, but I think the question is still valid since part of finding your PAP on a measured ball is based from the center line, which, as I am looking at it, varies slightly depending on the answer to the question. 

Yes, checking a drilled ball. Avg the difference... sounds good. That's actually what I've done in the past, but was hoping to figure out was everyone does. You are right though, if I avg the difference, the result should be close enough for govt work unless I know absolutely sure the accepted standard..... As for PAP different on each ball, you are correct AFAIK. In fact, a recently drilled ball was way different than what was previously measured. Went from 4-3/4 by 1/2 to 4x1. Hence my previous post called "flare in the air", which is a real phenomenon, at least for asym. I haven't proven it on sym yet, but that's another topic.