I dont trust the digital gauge. I use the gas cubby app and it seems like the digital reading overshoots by about 10%.
My maximum mpg is 22.8 according to gas cubby (calculates based on how much you fill up and how far you travelled) but the digital reading in the car was 25mpg.
If you have DCT, once the engine warms up and you drive for long period around 70 mph, you will get about 22-24mpg actual.
BMW M3 E92 - Silverstone II
BPM Sport Stage II Tune + Test Pipes, GTS DCT Tune