Can someone explain to me spine deflection. Is there a inch/pound equation. If I buy a spine scale does it measure in inches or pounds? can i build one and save myself a hundred bucks or so.

First, let me say that I don't pretend to be the one who should try to explain this to you.  A spine scale measures the bend of an arrow at a set length under a set pressure.  The standard scale is using a 26" arrow with 2 lbs of weight applied to the middle (either by hanging a 2 lb weight or having the same push down on it.  The deflection is measured in inches, ie 500 deflection is half an inch.
And the answer to the second question is, yes you can.  I built my own for $20 or less.  I used this model with my own modifications.

http://www.jamesmhill.com/Spine_Tester.html

Thank you. That helps alot. There is a lot of info there. Now I have to go out and find a dial indicator  

You can get a dial indicator at harbor freight

Actually the uprights of a spine tester are 26" apart and the arrow used is 28". You hang a 2# weight from the center of the shaft and measure the deflection. With wood arrows, for each inch over 28" subtract 5# of spine weight and for each inch under 28" add 5# of spine weight.
Google James M Hill spine tester. He has everything you need from building the tester to the deflection table in thousandths of an inch as related to the spine weight in pounds (.464=56#)

You forgot to mention that the spine, in pounds, is derived by dividing 26 by the deflection.

I wrote a paper that explains the wood and carbon/aluminum systems of measurement and goes through the math.  If you want it give me an email address.
Kevin

Kevin,
could you email one to me also.
Thanks, Rick

rcombs18@twcny.rr.com

hi,kevin i would love one to.maybe you could post it. manny718@comcast.net

Thanks Cupcake,

My email address is csdqm2@hotmail.com
Thanks again to all.