Continuing the theme of measuring atmospheric relative humidity, and adding gaining some insight into cross grain movement of wood as relative humidity changes and its effect on wood is the device I made below. It was made as a learning tool for students during the timber technology subject I introduced them to.
On this device is a Rittenhouse Hygrometer, the bent wand fixed to the bottom left of the base made in the same manner as Des described.
The two pieces of cross grain wood sitting vertically at the centre are oak to the left and mahogany to the right. The long grain of the two bits of wood are orientated horizontally. The two approximately equal size and pivot pointed wands, the ends of which rest on the top of the wood samples move in response to changes in the wood's width (cross grain dimension) and any change in dimension is magnified at the arrow points by the moments about the point (pivot). The end of the wands were held firm to the ends of the wood samples simply tying a bit of fishing line to the rod somewhere beyond the pivot point, adding a nut or two or something similar to the other end of the line and putting the line and nuts over the top of the device to hang down the back. Inked marks show on the paper attached at both ends of the back board where students had noted the position of the arrows after putting the device in different areas for a period of time, e.g., out in a dry but unheated shed, inside a heated office, etc.
Whilst this device couldn't really provide scientifically accurate data it was a great tool for demonstrating graphically key facets of timber technology for learners, e.g., the relatively large change in dimension of oak compared to mahogany as the samples' moisture content changed in response to changes in relative humidity. Slainte.
