By gps I mean making sure the the miles traveled on the odometer matches what the GPS is says for distance. I use a speedometer/odometer app and compare. I believe the odometer is acceptable to some 10% either high or low form the factory so just cause it is new doesn't mean it indicates the correct mileage..
For a mpg test you will have to fill up at the same pump you made the start fill up at. Like doing a circle. The vehicle will have to be pointed in the same direction on both fill ups. This eliminates pump quantity calibrations which again could be off and still be in specs from one pump to another. Then the direction point is so you eliminate tank slope meaning if its sloped one way it will accept more than sloped another way.
MPG is a real scientific process and you have to eliminate all variables possible for the readings to have any real weight.
