Help, 3 thermometers, which of these is right???

I can't figure out which of my thermometers to believe at this point, because the readings diverge as temps get higher. Anyone have advice on what it going on??? Here are the details:

#1 is a metal dial thermometer, #2 a Taylor 9842 digital waterproof thermometer, and #3 is a lab thermometer (which is supposed to be perfect AFAIK). I have tinkered with calibrating the metal dial based on the lab thermometer, and I just got the Taylor and ran a comparison test with all three with weird results.

In ice water, all three were within a degree, lab & dial at 32F and Taylor at 32.8F. BUT here is the problem: at mash-like temps, lab & dial were at 150F and Taylor was at 156F. Then, at boiling Taylor was at 214F, while the dial was at 202F and the lab was in between. I know the lab therm is supposed to be fully accurate, but I can't figure why the boiling temp came in at 208F at normal altitude. Or why they are within a degree at around 32F, but off by 6 degrees at higher temps. Any ideas???

first what do you consider "normal altitude"? 212 is boiling at sea level and are you using distilled water to do your boil test.

chances are all your thermometers when manufactured where calibrated for 32. each of your thermometers for what ever reason have different sized degree marks. you are just going to have to deal with it. take (212 - 32)/(boiling temp - freezing temp) for each thermometer and multiply that by what ever your reading is for that thermometer.