The "virtual" sensors (core, surface, ambient) override the "T" sensor markers.
One of the lower sensors (T1-T4) will almost always be labeled "core." That's the lowest internal temp.
With the thermometer inserted, one of the sensors will be labeled "surface." That's the actual applied cooking temp, and it shows the rate heat is transferring into the food! Super-useful, especially for slow-cooking. The internal temp will never exceed the surface temp. Hold that surface temp steady for edge-to-edge perfection.
The "ambient" measurement shows you the temp near the food. This will often be significantly lower than the set temp of your cooking appliance. That's not an error!
Food creates its own "weather" system because of the water evaporating - there's an invisible cloud of steam that surrounds the food, called the "boundary layer." With larger foods (e.g. roasts), this boundary layer can easily cover the T8 sensor.
The boundary layer is your friend - it steadies the temp, keeping the food near the surface from drying out or overcooking.
The fan in a convention oven will disturb the boundary layer - that's also why convection ovens cook stuff faster and create a crispier exterior.
The risk of convection is (especially with large foods) that the food will tend to become overcooked near the surface.
They're great for french fries though.
