This is not rocket science. Affix your probe to the underside of the tank glass and set it at 90 degrees F. Then check the temp at the glass inside the tank, and again on top of your substrate. WalMart has an inexpensive infrared thermometer which is decent and will give you an idea of the temps. Believe me, if the temp is just 82 on top of the substrate your snake will be able to digest with no problem. I've unplugged the heat tape on my adult corn rack when the ambient room temps hit 80 degrees during the summer, and the snakes don't miss a beat at feeding time. 90 degrees at the glass won't scorch a snake, and if you feel the glass you will barely even notice the heat.