I have acquired three digital thermometers over the years. I became suspicious of their accuracy, so I gathered them all together and let them rest with their probes all in the same place. Here's an Oneida showing 72, a Pyrex showing 68, and a Farberware showing 66.9. Before this test I polished the probes and jacks with steel wool. Are these like digital cameras that are expected to crap out over time? How long are they expected to last? Is there any way to tweak them to a correct reading, like zeroing a scale? Could this simply be a battery power level issue?