Real easy to make the protractor or dial indicator type. A lot cheaper and just as accurate too. Just another option to consider.
You could also make the pointer type like in the catalogs, but it's a good bit more work. Someone here just made one and posted pics. Looks REAL nice. It's about the only spine tester I've seen that actually looks like it should cost a hundred dollars or more. I think most are way over priced when you consider what you can make and how easy it can be. Although, this guy's didn't look easy to make. It looked better than any I've seen in the catalogs. Mine doesn't look anywhere near as good but it can spine arrows to the pound.