Hi Derek,
Press the black button (Number 5 on the diagram) to change from total miles covered (Odometer) to trip meter.
Press and hold the same button for a few seconds and it will zero the tripmeter.
I do that every time I fill up and run the car with the trip meter, rather than the mileage displayed and then I usually fill up again when I have done about 250 - 300 miles.
I hope that helps.