depending on the thermostat. A herpstat 2 has 2 probes and control 2 different systems. I personally have a herpstat pro and it does 4 different heat sources. I do like the johnson controls A419 thermostats aswell. You don't have to spend a fortune to get a thermostat. I do know the more you spend the easier it seems to be to setup the thermostat. I just got rid of my ESU thermostat due to the fact adjustments on a dial is a pain. With it being about 5 degrees colder you may be able to put it in a bottom tub remember heat rises. I know my racks the tubs closer to the floor are 1 to 2 degrees different. I don't have any reptile basic racks so i don't know how there units vary from level to level. I would imagine about 1 to 2 degrees is probably standard.