Like was said, all that matters is to fill your tank full either set trip meter or record odometer mileage, drive, refill tank to full, divide gallons used into miles driven.
Example: I drove 475.9 miles on 16.08 gallons of gasoline, which comes out to 29.6 MPG.
I don't use odometer, I use trip meter. Simpler that way.
tjgray3 
Threaded Mode
