This is what I use. It's just a 1x2 with grooves cut into it. In the photo showing I think is pulling at 26". For weight I take the tiiler gizmo out of the vise, put a bathroom scale on my bench and place the bow and stick onto the scale and release the string from the stick, pull down to desired lenght and observe the scale reading. But be carefull it could slip off and smack you on top of the head......
I have to build a proper gizmo that has the pulleys and a fish scale. Most everyone will tell you that the final tiller is pulling it in front of the camera and/or mirror. Then ya the proof is in the pudding.......sir..!