Chief.....if i remember right, the mfg. tolerance for arrow spine is .005" . An arrow with a .400 spine can have a .395 or a .405 or anywhere inbetween and still be considered .400 spine.

Arthur.... I made my spine tester from an Arizona arrow straightner. Just made a longer channel. This confirms my " bearing" test results that Chief does. Anyway, when testing my spine deflection on my cut and fletched arrows with the weak side up, i can get as much of a difference of .020" in a dozen like you. Now, with the supports 27" apart, take the arrow with the stiffest reading as your benchmark. Take the other arrows and take the measurement of each one. If you move the supports closer to each other, the reading will change to the stiffer. The trick is to get the supports adjusted to get to your benchmark reading. Get them the same. If you had to move them 1/8" inch (26-7/8" ) then you would cut that arrow 1/8" shorter. Move to the next arrow and do the same thing. When you' re done with the dozen of arrows, you will have a set that deflects the exact same amount. If you have a problem with weight (1/8" won' t weight that much...maybe 1 gr.) you can adjust as you normally would. The only problem I can see....someone mentioned resonant frequency wouldn' t be the same. That one was way beyond me (I' m not an engineer). Any thoughts? Anyone?