I always like to use the same gas station-- and the same pump--- that way when the pump AUTO shuts off--- its the same pump and it should shut off at the same point.
How to Calculate MPG
1- gas up. Let the pump auto shut off preferably.
2- Write down the current ODOMETER reading OR reset TRIP A to 0.
3- (You may also want to write down how much gas you just spen- and how many gal to fill up).
4- Drive.
Lets say you gassed up on Sunday- Odometer read 60,000. Trip A reset to 0.
You drive for 1 week.
The following Sunday- youre now at 60,300 and Trip A shows 300.
you return to the same gas pump.
You beging to gas up.... and you let the pump auto shut off.
You write down the number of gallons of gas it took to fill up/auto shut off... Lets say the pump shows 15.7 gallons.
To get the MPG--
you take the 300 miles you drove- and divide it by the 15.7 gallons it took to fill up.
300/15.7 = 19.10 --- so for the previous tank of gas-- you averaged 19.1 MPG.
When you go on your trip-- you may get slightly different MPG numbers because the Pumps auto shut off at different points... some may pump more or less fuel.. slightly skewing your MPG numbers.
But it should give you a good idea of your MPGs.
Just go on your trip- fill up at a station- reset trip A meter--- drive.
reach another gas station- gas up till it auto shuts off-- and calculate the numbers.