On Thu, 20 Jul 2017 09:42:10 -0400, "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.
No, steve. You are wrong. The amount of fuel you put in is the amount
you can squeeze into the empty portion of the tank. The amount you
used is the amount that used to be in the tank. You need to fill it to
the exact same point each time to get an accurate reading. You may
have filled your 72 liter tank to only 71 liters the last time you put
in 50 liters to fill the tank. Now, at a different station, with
different levels, you may squeeze in 73, or only 68. COSISTANCY is the
key - and where most will fall down, because, like you, they just
don't REALLY understand.