Reptile heat cable?.?

I choose middle positions so that you have an average temperature. The upper ones will be a little warmer because they are higher, the lower ones cooler due to being near the floor but on average they will only vary by a few degrees. I place the probe on the shelf outside the tubs near the heat tape or cable. Since most racks have the tub back against the heat tape, you want the thermostat probe to sit near the cable so that it doesn't get too hot. Once you set it and get it stabilized, you can check the temps in the tub with a probed thermometer or laser thermometer (easier to use, just point and read). If you need it warmer, move the probe a little further away from the tape or up the temperature on the thermostat.