I bought the CDN DTQ450X, which was one of Cook's Illustrated top thermometers.
It says you can calibrate it by putting it in ice water, holding the cal button. I always get "ERR" on the display. It says it will do that if the water isn't between 30-34.
I have the water very very icy and have let it sit in there and the lowest it will read is 34.8. I am holding it so the tip doesn't hit the bottom, otherwise it is warmer.
It seems like this therm is off and I can't calibrate it.