Temperatures are taken on top of the substrate with a digital thermometer with a probe. On the cool side is a second digital thermometer with a probe and a hydrometer. I've got the temperature figured out which is a relief and the under tank heater is controlled using a rheostat. The under tank heater isn't attached to the glass, it's sitting on a piece of tile with the enclosure supported above it. Is my thermometer probe in the right spot? Thanks for all the help.