Accurate thermometers.

[mike31154]

I have one of almost every type monitoring my tank. Two digitals, one conventional and the cheapo stick on. They're all within a degree or so of each other. Need to remember that the location of the sensor/thermometer will have some influence over the reading. The sensor probes for my two digitals are closer to each of my two heaters than the conventional and stick on, so I expect them to read a tad higher.