Please someone explain to me why you are putting the probe directlly on heat sources? Is this so ya dont have to use a vacant tub? I just dont get it. Onall my racks i have the probe in a tub. I keep 90 hot side and 85 cool side. I just dont get why you would play a guessing game by putting it on the heat source. You want to detect temps where the animal is living. Now i do agree the most important thing is ambient room temps. My snake rooms stay at 80 to 83. About 12 years ago i was having issues that were due to dead spots in the old flexwatt. But i havent had problems in it recentlly. Different racks need higher ambient temps to be stable.depending on how they are set up. Believe it or not my melamine racks are more reliable then my visions or freedom breeders in the heat dept.