That's something I make sure, mainly reading the difference between the temp gun and what the thermostat is reading, so far the temp difference isn't that bad, maybe .5 of a degree. I have a BN-LINK thermostat that was advertised to be used for germinating purposes, but works for reptiles as well (which I plan on replacing in the near future, but it's working quite well) and it only recommended not to expose the probe to water, but I believe it can be submerged in soil. Or at least that's what the instructions say.