RE: Spine???????
Spine is the stiffness of the arrow. It affects how the arrow absorbs energy from the bow, and travels forward to the target. It is measured by placing an arrow between two supports (24" apart, I think), and hanging a 2# weight from the arrow's middle. Then the amount of bend is measured. Underspined arrows would bend too much, and would be difficult to control. They would continue to oscillate for a good distance downrange. Underspined arrows are very difficult to tune with broadheads. Overspined arrows are too stiff, and don't bend enough. In my personal experience, this does not seem to be much of a problem for a compound bow shot with a release aid. I did build a spine tester 2 years ago, and found that some all carbon arrows vary quite a bit when you compare the stiffness at different places around the shaft, and also vary a lot when comparing different shafts out of a dozen.