Yes these digital thermometers seem to be off sometimes. At least the inexpensive ones. I brought home a good old fashioned floating mercury thermometer. I shall put it in my tank and see which thermometer is telling me the truth.

2.5 degrees may not seem like a big deal but...... If your tank is over heating or close to over heating the difference between 82 and 84.5 could mean the differenence between life and death especially for SPS stuff.

I still have some SPS that are recovering from my 3 day overheat. My tabletop which was doing just awesome (until last week) has RTNd a bit but is hanging in there. Only time will tell.