I bought a digital from Sur La Table to make the Salted Pumpkin Caramels.
First--It became possessed when I was washing it/steralizing right out of the package. My EE husband got it under control and blamed me for its posession. Machines never misbehave, its the user. :-p
However, when making the caramels, as the temperature was rising from boiling, the thermometer was reading that it was lowering, and eventually just went crazy.
So, I'm happy to know the original posessed behavior is explainable.
Anyway, I found that the readout was not legible when the device heats up.