After I discoverd that my odometer was under reporting milage by about 2% I decided that the most accurate method to determine mpg is the computer read out on the dash - at least with my NAH.

Now I read this article on AP's website:

http://hosted.ap.org/dynamic/stories...MPLATE=DEFAULT

which makes hand calculations even more suspect.

 

The computer always gives me around 2.1-2.5 mpg higher reading than what I get from hand calculations.

The odometer being off by a little bit is quite easy to accept... after all if you inflate your tires a bit more so their diameter becomes just a tad bigger, you are traveling longer straight miles distance than your transmission can count based on revolutions. In other words, if you want to keep your warranty for a long time, get 20in tires :-) LOL

 

Here is part of an email I received from someone I know about this same subject.

This is a true story, so read it carefully. On April 24,
2008, I stopped at a Kangaroo

BP gas station, located at 1325 Main Street, Cartersville,
GA. My truck's gas gauge was on 1/4 of a tank. I use the
mid-grade, which was priced at $3.71 per gallon. When my tank is at this
point, it takes somewhere around 14 gallon's to fill it up. When the pump
showed 14 gallons had been pumped I began to slow it down, then to my surprise
it went to 15, then 16. I even looked under my truck to see if it was
being spilled. It was not. Then it showed 17 gallons had been
pumped. It stopped at almost 18 gallons. This was very strange to
me, since my truck has only an 18 gallon tank. I went on my way a little
confused, then on the evening news I heard a report that 1 out of 4 gas stations
had calibrated their pumps to show more gas had been pumped than a person
actually got.



Here is how to check a pump to see if you are getting the right
amount:

Whichever grade you are using, put EXACTLY 10 GALLONS in your
tank, then look at the dollar amount, if the dollar amount is
not EXACTLY 10 times the price of the fuel you have chosen,
then the pumps are rigged. In my case as I said the mid-grade was $3.71
9/10 per gallon, my dollar amount for 10 gallons should have been $37.19.
If I had only check the pump. It doesn't matter where you pump gas, please
check the 10 gallon price. If you do find a station that is cheating,
contact the Georgia Agriculture Department, and direct your comments to Tommy
Irvin, Commissioner. In other states contact proper
authorities.

 

If the pump is not calibrated, how do you know that you are putting exactly 10 gallons of gas in your tank? The problem seems to be not that they are charging you more for gas, but rather giving you less gas than they tell you they give you.

There was a recent article on that same subject, http://www.thestate.com/business/story/386823.html

My favorite part of the article, "
Bob Wolfram knew something was wrong when the pump he used in Davenport, Iowa, showed he put two more gallons of gas into his tank than the tank holds.
“I was low, but it wasn’t negative,” said Wolfram, a 54-year-old engineer"

 

I would purchase a 1 or 1.5 gallon gasoline container. Then mark the line on the tank you know to be 1 gallon (these portable tanks usually hold more than what they are rated). Go around and check various stations your frequent.

 

In Florida, accuracy of fuel pumps is regulated by the
Florida Deptartment of Agriculture and Consumer Services,
Division of Standards, Bureau of Petroleum Inspection.

Contact Information:
Telephone: (850) 488-9740
Fax : (850) 922-6655
Field Office Telephone: (850) 487-2634
Postal Address:
Bureau of Petroleum Inspection
3125 Conner Blvd.
Lab 1, Mail Stop L29
Tallahassee, FL 32399-1650
Web site:
http://www.doacs.state.fl.us/standar...o/contact.html

Every state has something similar.