In my limited (5800 miles and 1 roadtrip) experience, the trip computer is more accurate for long drives w/in a tank than lots of short ones. Long distant trips register w/in a tenth or so per tank, but the dozens of little regular trip w/in a tank are usually lower by 2-4 mpg than manual calcs at fillup. It also seems that wide swings in average over a tankful can be misrepresented as well. For instance, you start off in low to mid 40mpg range over the first 100 miles, and slowly work it up to 50mpg at 500 miles, the display is too conservative when compared to pump math. I suppose it's better for the car to report conservative rather than optimistic. I'd hate to do the math and be frustrated!

W. Marc Schmitz
06hchII MagPearl