There are some good YouTube demonstrations of how to make a cheap spine tester. Mine consists of a couple of nails, a 2 pound weight and a digital caliper. The charts are online for printing and downloading.
That being said, as far as I can tell, the spine charts are meant for center shot bows with straight shafts. I have been shooting a traditional longbow which does not have a cutout center shelf for the arrow, so that is strike one against the spine charts. I have also been experimenting with shafts cut from trees and bushes. These shafts are naturally tapered and so the spine chart doesn't apply to these arrows either; strike two. Finally, some of the arrows are made from hollow stems so I have to put oak foreshafts on them, that is not covered by the spine charts either; strike 3.
So, I make the arrows, I shoot the arrows. I don't worry about spine weight.
Buck67