Can't trust only one Thermometer

[Cujo#31]

I refuse to run a heater without a controller to monitor the temp, and as an added redundancy my chiller is running on its own settings. That way it requires 2 system failures. As well as replacing heaters every year to make sure they are in as good condition as possible.
I also use 2 glass thermometers, one in display, one I. Sump, and I have a digital temp gauge so that I can check tank temp on controller plus 3 separate thermometers.