I'm another who agrees with Black Frog. I'd go even a little further in my estimation of importance of spine. I've found that when I spine test my carbon arrows, I end up with much better shooting arrows than if I don't. I trim from both end when possible and cull the arrows with spine ranges that are too far out from the average. Then, I test for the stiffest side and align the cock feather with that mark. Last, I make sure the broadheads spin straight. Combine all this with helical fletching and I've been able to get some really crappy carbons to fly amazingly well. I don't even test straightness, other than spinning the broadheads.

The difference from doing this and not doing this, has been night and day for my broadhead flight. I'm really quite satified shooting the middle grade of Gold Tips, that I normally wouldn't even touch without doing this procedure.

As a side note, Black Frog's spine tester is amazing. Mine has the indicator mounted underneath the arrow, so the spring does affect the reading. I've realized that I don't really care, because when I'm testing a dozen, I'm looking for consistancy and it does measure that. I don't care if the actual numbers are .309 or .306. I just care that I can compare one arrow to another. Now, if you're making arrows for others and someone orders a spine of .342, you don't want to send them .375. The only place I know where this might happen, are guys making traditional wood arrows for others.

If you decide to make one, I definitely recommend that you follow his design and hange the weight below the shaft and mount the indicator above.