My thermometers vary also. The one that came with the bator that lays on the eggs stays pretty much at 99.5. The meat termometer I put inside stays about 2 deg cooler. The one an top the bator is all over the place but usually low. I assume the variance is normal because of type differences. I am going in to town today and will probably pick up a cheapie one that is similar to the one that came with the unit and see if that registers the same.