Sling Psychrometer
Humidity was involved in microwave EDM reductions. Not sure there are any of those around any more.
I have not seen any normal formulas for astronomy that use humidity, but suppose it might exist for geodetic astronomy.
As I said, humidity is a factor in computing refraction at microwave frequencies and was part of early satellite positioning reductions such as doppler which probably operated in the VHF frequency ranges. But I have not seen it in any GPS reductions.
You want to chain with care using conventional tapes, you need pull scales for pull and tape thermometers.
EDM's can probably be kept going for at least a few years with solar chargers or similar alternative sources, but GPS loss would require a lot of people to start looking for those old T-2's and DKM2's with more appreciation, and few would really know or want to follow the procedures to use them, almost a lost art.
- jlw