Don't know about calibrations but if you look through your grill you'll see the thermbulb for the outside air reading. Out of necessity it's mounted on the radiator bulkhead so.......I'm thinking that it may always be catching a little engine compartment heat especially when at slow or no speed. Once moving the cooler outside air would hit the bulb first and the hot engine compartment air would end up exiting the car near the firewall giving you a more accurate reading. Calibrating it for slow or idle conditions would simply make it read low when the car starts moving again. Just my thoughts. I've been full of hot air before......hot air! Oh Christ I better start drinking again!