Lower the number the more straight it is. I believe it's called run out. I can't tell you the exact specifics on how long the arrow needs to be and all that without looking it up. But basically it means if you put an arrow of a specified length on an arrow spinner and put a dial indicator on that arrow the dial indicator should not move more than the specified amount along the distance of the arrow.

If I am wrong about this someone please correct me. I know how to do it because I used to run screw machines, but I don't know the standard for arrow manufactures. And I have never actually done it to an arrow. I just put them on a spin tester and eyeball it. If they are bad you don't need a dial indicator.

Paul