I was just searching around the net for AMO standards, and I think I found out why the orginal charts for this spine tester were so confusing. Check this out..
http://archerysearch.com/publications/AmoStandards.pdf This looks just like the original protractor charts...values rounded off to hundredths instead of thousandths, different values for different draw lengths, values only going up to 70lbs. Not only that, but there are different values for target arrows vs feild/hunting arrows. Talk about confusing. If this is what the author had to work with, I think he did a pretty good job.
Here is what I based my chart on...
http://www.rosecityarchery.com/amospine.html The second chart simpler. But BOTH of these web pages are supposed to be AMO standards. Makes you wonder, when you buy a dozen shafts spined at 55/60, what values and what charts are they going by??? I thought AMO standards were supposed to be standard, LOL.
Austin