Due to the location of the lid therm, it will almost always be different than the grill temp. If you pull the lid therm and test it with both ice water and boiling water, you will probably find that it is very close to specs. This last weekend my lid therm was at least 20* off from my grate temp. I will always go with the grate temp and only look at the lid therm as a curiosity. I am sure my lid therm is close to spec and I don't care. I only care about the grate temp and the meat temp. The main thing is you have to decide which you want to use, the lid or the grate temp. Once you decide that, don't worry about the other. Good Luck.