What you are experiencing is normal when you attach a thermostat probe directly to the heat source. The heat source has the ability to heat up quickly overshooting your target temperature at which point the thermostat turns off the heat. Then the heat source cools down quickly and undershoots the target temp. During this “teeter totter” effect the enclosure itself is not actually getting up to temp and the fluxuations on the thermostat can look wild. By placing the thermostat probe inside the enclosure over the heat source it will buffer that effect and although all thermostats initially will require some regulation time it will be much smoother. In some enclosures giving a couple of inches of space between the probe and the hot spot ends up being the proper placement. In any enclosure the probe placement will be the #1 key to having a smoothly regulated environment. Every enclosure is unique and will require some small experimentation on the owners end and for safety its always best to set up new enclosures without the animals in them until you achieve regulation.

George