I think it has something to do with the momentum of the fuel in the tank...When I take off really hard at 1/2 tank full, It´ll rise to 3/4 tank, and if I brake hard it´ll drop back to 1/2 tank, even though I usually know exactly where it should be by my trip odometer. Right now I´m right around 155 miles, so I should have just over 1/4 tank. (my gas mileage sucks ass, I only got 15 mpg last I filled up, and usually I don´t get much over 19 mpg)... when I see that, I usually just drive like an insane psychopath anyway. what do I care? I´m getting worse mileage then a Mustang GT.