Spine.
I have read alot about it and i did alot with it to.
Now that you brought up the topic, i went back reading againg.
I think one of hte most underetimated things in archery is spine.
More to the fact that where we find constant innovation in bows, the arrow has not changed in shape in thousands of years.
Spine did alot for my archery.
We are all to much hanging at the Easton lists i believe.
If easton says it true, its true.
Easton measures spine at a 29" shaft lenght over a 28" span.
In the middle of this 28" span they hang a 880 gram weight.
Than they measure how much this shaft is bending.
Well, thats a simple thing to build was my opinion, and so i did.
I worked a bit with mirrors and clocks there i had a ' spine tester'
Maybe it had been better if i didnt build it, because its something to go crazy about.
I found out about the difference in spine between alu' s and carbons, brand X to brand Z.
After shooting a easton alu arrow in a foam target for 10 times it lost for about 40% of its natural spine!
After those 10 times they become weaker and weaker but not so fast as when they are new.
This told me i had to be very secure about strait impact.
Another thing i learned is the fact that when you start to compare new carbons out of the box you better make sure you are very, very good friends with the shopowner because in a set of 12 ACC i had 4 same sized arrows!
Now i have to say that the difference between the arrows is so little that I dont believe there is anyone in the whole world that would see the effects of this.
I even dont believe that a shooting machine would notice.

What i did with it?
I found out i could easy go 1 to 2 sizes lower in weight that Easton tells me.
Therefor i get a wide variaty to play with where it comes to point, inserts, vanes, nocks, FOC' s, arrow weight etc. etc.

Strait flying arrows is what i like to see.
And thats is all about spine.
And that my friend, is what makes archery my favorite thing for the last 30 years.