Flexure mechanism that helps turn a cheap photo-interrupter and a razor blade into a repeatable displacement sensor. The dual diaphragm flexures constrain the motion of the razor blade such that it moves in a very repeatable linear motion....aka good stuff :)

For less than $10, I've consistently seen on the order of 1 micron of repeatability…granted, this also requires some care on the electronics side of things. Also, if you don't have some pricey calibration gear on hand, it may be tricky to actually make use of that repeatability, since these photo-interrupters aren't always all that linear.

I'm not sure how much interest there is in these sorts of things, so I didn't think it worth a detailed "how to", but if anyone is interested in knowing more, hit me up!