On Thursday, July 20, 2017 at 9:42:15 AM UTC-4, Steve W. wrote:
wrote:
On Thu, 20 Jul 2017 12:08:33 -0000 (UTC), Mad Roger
wrote:

What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Repeatabilty is terrible. Accuracy can be pretty good over multiple
tanks. Can be pretty good even on single tanks IF there is a way to
ensure the tank is always filled to EXACTLY the same point (like a
level in the fill - tube, with the vehicle parked at EXACTLY the same
place for each fill-up). Relying on the auto-shutoff of the pump can
cause variance of several liters per fillup.

Vehicle position or the auto shut off point won't make any difference.
You read the amount of fuel you pumped off the pump itself. The only
real issue is odometer accuracy. That can vary with tire size variations
and factory calibration.

--
Steve W.

Of course vehicle position and shut off point makes a difference.
If you fill it up in a situation that winds up with more gas
in it, then fill it up after your run in a situation that winds
up with less gas in the tank, you think you used less gas than
you actually did and you get slightly higher MPG.