Just wanted to add that I am using a glass tank too but with a heat mat and thermostat set up. I originally had the thermostat probe in the hide next to the digital thermometer probe. All was well with that for a few days but as soon as he realized he could burrow I started getting discrepancies as much as 5 degrees between the thermometer and thermostat readings (he was knocking the thermostat probe out of contact with the glass leaving it measuring air temps instead). What I am doing now is placing the thermostat probe under the tank in direct contact with the UTH and measuring the in hide temps with a secured digital thermometer probe. I find that there is a standard 2 degree different between the mat and the glass temp reading but adjusting for that has allowed me to correctly set the thermostat to whatever will keep it at 90 in hide. There is a marked difference between glass temps and the surface temps so since I know he likes to dig down anyway I have cleared out a coiled snake sized area on the glass in the hide. He curled right up in it and things have been stable since.