Yep! Took me a spell, but that' s about what I' ve figured out too. Differences in terminology.

My spine (flex) tester is a couple of 1X6' s. One as a back and the other as a base, with 1X2' s mounted upright, 26" apart, with ' V' notches cut in the ends to hold the arrow shaft. I' ve got an arm made from flat steel loosely bolted to the back with a large bolt at the other end of the arm holding enough washers to make up 2 pounds of weight. The length of the arm is such that the weight will fall in the center of the shaft when it' s on the supports. A 1" travel indicator that measures to .001" is mounted to the base directly under the wieght and centered with the arrow shaft.

I don' t have it all worked out to where it will give exact spine, but it does great for checking variances between one shaft and another. Or variances around the same shaft.

Actually, at 26" between centers, mine is set up for wood arrows. For carbon arrows the supports should be 28" apart.