I have two thermometers/hygrometers (one from Lowes and one from Target) that were in the $15 range (by memory). It's been a while since I purchased them. They both do temperature and RH, and both have max min functions.
I also have a Fluke hygrometer that was quite a bit more expensive (about $150) that we use in our homewatch business. It also does dew point.
Whenever I have compared them, all three have been within 2 degrees F. and within 3-4% RH. I have not done any sort of calibration curve comparing them through the temperature and RH range.
The cheap ones I'm comfortable leaving outdoors overnight to get a min temp. The expensive one, I treat pretty carefully to protect the sensor. If a cheap one gets sprayed or rained on accidentally, it's not a major issue. The cheap ones react MUCH more slowly to changes, especially RH changes, and have to be left in place for 5 minutes or more to equilibrate and give a stable reading. The Fluke is near instantaneous.
For the small (if any still exists) price difference, I think I'd go with Ray's hydrofarm unit. The brand is designed for gardening use, not normal household conditions, so is probably less likely to be damaged with normal orchid use.
Last edited by BobInBonita; 01-22-2011 at 04:14 PM..