Can't trust only one Thermometer

[Synthesis]

I fully agree. I was skeptical of a glass thermo I was using because it would always read much higher then what I was setting my heater to. I could not for the life of me get the heater calibrated while using the thermo. So I went out and purchased a similar, slighlty better, thermo. Sure enough, it read 2 degrees cooler. And much more accurate to what I was setting my heater to. I still run both and make sure the deviation between the two is the same at all times to help ensure both are still functioning normally.

With temp being so important, redundancy for this "parameter" is a must.