Well, on the assumption that that is correct, I edited all my tanks to use the computer's calculation for mpg (we've been writing that down, along with the odometer reading, on all the receipts). Went from 27.8 average to 29.1!! Is this real, though? If I take the number of miles on the odometer, and divide by the number of gallons of gas we've purchased, it comes out to around 28 still. This isn't making sense again.