I checked my mileage computer against the real MPG numbers (actual gallons and miles driven on 3 full tanks, about 900 miles of normal driving). The mileage computer said 19.8 MPG at an average speed of 26.2 (mostly around town stop and go driving with a little highway) and the actual real MPG is 19.2. Mileage computer is with-in about 1/2 of a MPG.