Calibrating dome Thermometer

Saintrs

I recently messed up a pork butt and instead of juicy and tender, it was dry and hard. Not very good. The internal temp was 200 degrees in 5:30, so I thought my digital thermometer was broken. I knew that you are suppose to cook a butt for 1:30 to 2:00 per pound, so I let the butt sit for another 7 hours. Needless to say, not a good butt. The only conclusion I could come up with was the dome thermometer was off. Therefore, I calibrated it to boiling water and sure enough, the dome thermometer was 150 degrees off. My questions are: 1. Why would this happen? 2. My thermometer needle now starts between 100 and 200, see below pic. Is this ok?

Saintrs

Pic Has complications, so no pic.

lousubcap

Question #1-If you didn't wrap the needle around on itself during a pizza cook or hi temp clean I have no idea how it could get that far off since the last time you checked it.   #2-As long as you dialed it in for the boiling water temp then don't worry about what it reads at ambient. 

FWIW-I check my dome calibration before any low&slow-it's the one indication that will control the cook so I like to know it's all good.

Saintrs

Thanks. I am new at this so any feedback helps.

Grill Sargent

A pit master once told me to always run a separate surface temp gauge where the food is. Been practicing that for a few years now and much more reliable. >-