For my spine tester i just screwed two hooks underneath my work bench 26" apart, drilled a hole in the bench at 13" and used a gatorade bottle filled with water to equal 2 pounds. Place the arrow on the hooks, put a dowel through the hole so it rests on the arrow and then hang the weight on the arrow at 13". Measure how much the dowel moved and then using the spine chart from the link that Ed gave you, covert your measurement to pounds. Boom done.