Hi QuinteQ Thats what we did to get the correct mileage. We averaged 22MPG. The tank was filled and the trip gauge zeroed, and the trip meter zeroed. Drove the car really carefully. I expected the reading to be incorrect, but the amout staggered me. I also live in Wales at halfway up a mountain so realistically we have to expect low MPG, but the gauge read 35 MPG. I think my complaint is the trip computer is so wrong, not the MPG I get.