I was told that first you put it under the substrate under the warm hide to make sure the temperature does not exceed 95 degrees, then you put it on top of the substrate under the warm hide and adjust the depth of the substrate until the temp reads 92-94. Then if you want you can put it inside of the cool hide to measure that temperature. Then once you are certain they are safe and correct, you can put it back on the glass under the warm hide to monitor that as it is the most dangerous to your snake.