Here is a poor mans hygrometer... but it's a little slow, as I explain. Not that anybody needs proof, but here is a graphic example of how much wood CAN move when the weather changes and humidity with it. I took a worse case scenario, a species that is notorious for moving as the weather does, oak, and cut a strip off the end of a flatsawn board (flatsawn moves a lot more than a riftsawn or quartersawn board does). I wanted to see how much that cutoff would swell and shrink as the weather changed, so I then simply attached ONLY ONE end of that cutoff to a piece of plywood (got this idea out of Hoadly's book, Understanding Wood). The other end of the cutoff "floats" as I attached a hook which is attached to the very bottom of a large copper pointer, which is then pivoted a short distance above that. (see closeup pic of end of cutoff). So... as the humidity goes up, that piece of oak swells, which pushes the bottom of that copper pointer away from the oak, which (because it is pivoted on the plywood) moves the top of the pointer to the right. As you can see from the lines on the plywood showing the full range of that pointer over time, that piece of oak which is kinda "floating" and allowed to move, did indeed move almost half an inch from full swell (humid day) to full shrink (dry day). It doesn't move fast because of the relativly large size of the piece of wood, and it generally lags behind a relative humidiy meter by a day or so. In other words, if you take an RH reading every day and see the RH starting to rise, the wood/pointer won't react much for another day or so till you can see it start to move in that direction. I havn't taken the time to rig it up and test this, but I suspect if I had a much skinneir (but just as long) piece of wood with less bulk and mass, the meter would react faster. Call me nuts, but this kind of stuff interests me to no end. If I had the time, I'd have dozens of these little jigs set up with different types of wood, cut different ways and lengths just to experiment.