Continuing on the trend of making highly specialized luthier tools with whatever I have lying around, I made a thickness gauge!
It's a piece of oak, cut in the shape of a lyre because I wanted it to be more than just a plain [ bracket shape (and the whole thing with Apollo's lyre and god of music and all that, it's symbolic as well as practical), with a cheap but accurate digital caliper I had, some brass screws, rubber band, and a couple of burnt LEDs for the tips!
I considered putting a little lever on it but it's really easy to raise the measuring bit the way it is with a thumb or just pulling on it so I think I'll just leave it as it is, since it's working just fine.