'perzactly' - what you do to reduce the affect of variables is average 10
tankfuls for mpg.
Like the total miles divided by the total gallons. 

Even better, toss out the hi and the low extremes of a tank's worth, then
average over a number of 'more normal' tankfuls. 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
John Bange
Sent: Tuesday, April 22, 2008 6:40 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: MPG redux

>  I was thinking about this concept and I don't know how it can be relied
on
>  either unless you trust that the shut-off moment of the pump is the same
>  every time. There seems to me to be too many variables even with the same
>  pump to be able to rely on it.

Well, you can generally assume that even if there are several
variables, given a large enough sample the variations will average
out. None of the variables are going to skew the outcome that much,
and most of them are additive rather than multiplicative. A +/- 1
liter variation (that's a LOT) in shutoff point at fillup from 1/4
tank will only result in a .25 MPG variation. Granted, you will never
get within the sort of precision seen in the science lab, but +/- .5
mpg accuracy  over the long term would not be an unreasonable
assumption.

--
John Bange
'90 Vanagon - "Geldsauger"
'90 Vanagon GL - "Wiesel"

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