The first manual calc I did on our HiHy came out at 26.1 MPG while the computer was showing 25.3 MPG. Don't forget that ultimately gas mileage is nothing more than the miles driven divided by the amount of gasoline used in gallons. This is true for 10 miles, a full tank, or a year's worth of driving (the longer you go, the better the average).

In order for these two numbers to match, the computer must be reset at the station and the tank must be filled up to exactly the same amount as the previous fill up. This is very hard to do consistently even with the autoshutoff feature on the gas pump. I would be curious to see how the computer and the gas station data compare after one year, or even six months (I'll never know, I always reset mine).

His and hers hybrids, it's a beautiful thing!