On Wed, 19 Jul 2017 22:36:21 -0600,
rbowman wrote:

I use a Scangauge II plugged into the OBDII port. It's sort of accurate

I'm still looking for where I got that 4% accuracy figure for mpg
calculations.

This article describes the two-part problem correctly but the article
doesn't put a percentage on the results calculated at home.
How accurate are gas mileage monitors?
http://electronics.howstuffworks.com...ge-monitor.htm
"If your car's mileage varies by about 10 percent based on driving
conditions, how do you know if the improvement you see after, say, adding
acetone to your gas tank is a result of the additive or of the weather?"

Basically, everyone who gives you a MPG claim is wrong (IMHO) because they
actually *believe* their accuracy and repeatability to figures which are,
in reality, a figement of their imagination.

Sure, they can *see* the decimal places, but it's my current statement that
I need to prove that anyone quoting numbers within + or - 1 mpg is probably
fooled by lack of knowledge about what they're actually doing.

The two areas of huge inaccuracy a
a. The test conditions
b. The test equipment

I'll check out these references which are in the back of the article.
Allen, Mike. "3 Gadgets That Really Work." Popular Mechanics. DIY Auto.
December
2008.http://www.popularmechanics.com/auto...23.html?page=2
Allen, Mike. "How to Monitor Your Fuel Economy in Real Time on the Road."
Popular Mechanics. June 9,
2008.http://www.popularmechanics.com/auto...o/4267957.html