Black Frog, that is an amazing spine tester. Looks like you'd have to charge about $1000 if you wanted to sell one.

I love the design. When I was building mine, I did quite a bit of research and had read somewhere about removing the spring and mounting the dial indicator on the top. After thinking about it, I realized that I had no need to know the actual spine, that comparing arrows to each other was sufficient for my use, so I took the easier route. Mounting the weight below the arrow is a challenge and I wouldn't even want to try to make the gizmo you created. I also tried to imagine the amount that little spring would affect a 2 lb weight. I don't think it's much - especially on the stiffer spines. After looking at a few dial indicators, I realized they don't all have the same spring tension. You can choose one with less pressure. I'm not sure how far mine is off, but most .034 arrows hover right around the .034 mark.

I used 3/4" cabinet grade plywood with common hardware brackets. With the dial indicator it cost about $30 and an hour of my time. It works, but is no where near the tool you made. Wanna trade?