I don't know your bator but it looksike you set it to a certain temp and it tries to say at that temp.
It might work a little harder once you take your turner out which causes it to over heat some.
It's good that you know this...so you will need to turn it down some.
Keep playing with it with calibrated thermometers.
Move them around in your bator and leave it closed, after moving them, and wait a while and check their reading again.
I'm willing to bet the entire bator doesn't stay the exact same temp at all times.