When you scroll through with the left wheel the DIS should change. There is various info you can see, but the average MPG marked with a "1" is for the current trip. This resets itself with every journey (if you use the car in less than 2 hours since the last journey it will not reset but add the journey on to the previous one. The average MPG marked with a "2" is a longer term one and can be reset using the 0.0 button on the dash.