A thermometer is used to measure temperature. A thermostat turns your heating element off and on to regulate heat. Depending upon the size of the heat mat it may or may not provide an adequate basking spot. Also a heat mat generally should not be exposed directly to the snake - it should be placed under something else or even the cage itself. As stated earlier, keeping temps up in a glass cage is very difficult. I keep mine in melamine cages with heat panels however globes or ceramic bulbs will also do the job.