I hope that post didn't come off as know-it-all, I had a few samples of the raspberry cider before bottling that batch O_O. I never even realized a thermometer could be calibrated, so I wanted to make sure other noobs were left in the dark.
I couldn't get my thermometer spot on at both ends either. I split the difference, and yes I have a cheap a$$ meat thermometer. I was weighing the options of a) running to LHBS to get one, stalling the brew an hour, or b) calibrating. My guess is that if the thermo is off 4 degrees at 32F, and 4 degrees at 212F, it should be right on at 122F and "pretty close" in the 150 range.
In the end, if you are going to use a crap thermometer, at least calibrate it!!! And hey, the proof is in the pudding as I hit my OG right on and got full conversion of starch to sugar (iodine test).