I'll add in for emphasis.. Craig is 100% right on tstat and the thermometers. No heat source should ever be used without a thermostat to control it. (Not to mention the fire hazard unregulated heat sources pose)
Here's a video showing the temps heat mats can achieve unregulated in a very short time:
https://youtu.be/NcGJaHVF72w
Also, here is an example from a recent post somewhere of a burned ball python from an unregulated heat mat. This is a severe burn with potentially infection and other stuff going on.
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