My spine tester cost < $2.00. Most of that was the fee for printing a color image. PM me if interested and I'll send a PDF of the scale or just do a google search for "2jays" spine tester.
I didn't use the box method. I made mine so it could be wall mounted. So you only need a section of thin plywood or acryllic (free drops can be gotten from sign shops). My needle was taken from a bike wheel with stainless spokes. Your local bike mechanic will have several bike wheels rolling around by the trash can. Then a bronze bushing. Mine was walnut but I have a lathe. The weight is a jelly jar 3/4 filled with play sand from the local playground. I used the wife's digital kitchen scale to get the weight right.
It needs to be able to be zeroed out. Instead of making the arrow rest moveable I simply allow the scale to pivot with an elipse cut piece of the same material. Pivot the elips up and the scale moves up, pivot it down and comes down.
