Where's my MPG going?

[rningonfumes]

Okay, since the argument is accuracy...

This is what you do:
(if you are looking to compare mileage.)

1. Fill up at the same station and possibly at the same pump.
2. Fill up at the same time of the day, same time of the week.
3. Stop at the click, maybe more if you want to round to the nearest dollar- no more than that. I do it to the next tenth of a dollar.

Divide new gallons into current miles driven. Rinse, repeat. It does not matter how much you filled, nor that you can still even fit 1-2 gallons more, just have to have that consistency.

Edit: And for those who think that they are still adding gas when it clicks, there is such a thing as overflow that goes back to the pump..ie you've wasted gas by trying to overfill. This overfilling can also account for mis-calculations for mpg.