Which thermometer to trust

Did a Porter yesterday and was shooting for 153°. My Kettle has a thermowell with a probe connected to a Ranco PID controller. After dough in it read 152°, pretty close so I could have just winged it or heated it up. I look at the dial thermometer right next to the thermowell, it reads 158 :x Next I get the “lollypop” scientific thermometer out and it reads 154°, also close enough. Yes this was all after stirring it up.

I don’t worry much about stuff like this and always figured that if it is close, it will come out beer, better beer that I can get at the convenience store. I am inclined to trust the “traceable” scientific thermometer but also know if you poke any thermometer around in the mash you can get a bunch of different readings. What do you all think?

BTW the Porter is happily chugging along this morning and was within .002 of my target gravity.

Some think this is overkill, but this is what I do: viewtopic.php?f=5&t=109024

It’s not the cheapest solution, but it’s a breeze to use and I can’t imagine a more accurate, reliable solution.

I just calibrate the lollipop style from NB using ice water and check the mash also with a floating glass mercury thermometer, usually those are within a degree of one another. I should check my Blichmann brewmometer with a pure water sample against the others before roughing in, but I always seem to forget to do that.