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#1 2008-07-19 02:15:19

prius08
New member
Registered: 2008-01-10
Posts: 1

MPG calculation flawed

It is not reporting the correct MPG when putting in a new fill up.

When you mouse over the MPG column in history it is showing the correct miles subtracted but the divided by sometimes is more than the gallons of gas recorded and more than I could put in the car. Can not determine how it is getting the higher number.

With the following entries I made the calculations I expected and what I got on the site.

Miles / gallons = result |Site reports
383 Miles /8.591 Gallons  = 44.58MPG  |site reporting (11,748-11,365 / 34.888 = 10.978)

255 Miles /5.001 Gallons = 50.98  |site reporting (11,365 - 11,110 / 21.7 = 11.751)

364 miles / 9.598 Gallons  = 37.92  |site reporting (11,110-10,746 / 17.854 = 20.388)

and several more.   I noticed this problem started around 28 June 08 for me while on a trip and inputting multiple fill ups for a single day .   I only put in the Odometer reading,  gallons, price and  notes sometimes.

Can you recheck your program calculations please
Hope this helps track down the problem. 

Thanks for providing the site

Last edited by prius08 (2008-07-19 03:26:46)

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#2 2008-07-19 15:32:26

support team
Administrator
Registered: 2007-06-20
Posts: 188

Re: MPG calculation flawed

Dear prius08,

Thank you for reporting the problem.
We will investigate and get back to you.

Thanks again and have a nice weekend!

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#3 2008-07-22 15:53:11

support team
Administrator
Registered: 2007-06-20
Posts: 188

Re: MPG calculation flawed

Dear prius08,

We have implemented improved MPG calculation routine and updated MPG values for your car. Old routine was very date sensitive and was incorrectly calculating MPG when you have more than one fill-up on the same day. New routine is more robust and we believe the problem is now gone for good.

Have a great day!

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#4 2008-07-22 16:28:30

tankbeans
New member
Registered: 2008-02-28
Posts: 7

Re: MPG calculation flawed

I noticed today that at the top of the page, above the mileage graph, all of the statistics are reading zero. It said that I've driven 0 miles this month, and have used 0 gallons, which has cost me $0, for an average mpg of 0. Not sure if this is just a glitch caused by updating or not. Thought I'd let you know.

Thanks

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#5 2008-07-22 17:20:56

support team
Administrator
Registered: 2007-06-20
Posts: 188

Re: MPG calculation flawed

Dear tankbeans,

You are absolutely correct, that was a glitch caused by updates, and we almost missed it, thanks a lot for the heads up!

Updates are now complete and totals are back to normal.

Thanks again!

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#6 2008-09-10 06:31:46

thomjoyce
New member
Registered: 2008-08-18
Posts: 1

Re: MPG calculation flawed

I am having an issue also when I have more than one fill up in a day. It is showing that I have 158 miles to the gallon on two occasions. Can you help me on this

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#7 2008-09-10 12:02:58

support team
Administrator
Registered: 2007-06-20
Posts: 188

Re: MPG calculation flawed

Dear thomjoyce,

While looking at your vehicle's page _no_links_www.mpgtune.com/vehicleDetails.php?carId=2406
we noticed that fill-ups that you put only 2.812 and 2.670 gallons in a tank were most likely just to get by and you did not get to full tank on those fill-ups. There is a checkbox called "Left Gas Station with Full Tank" that was checked on those fill-ups (it's checked by default).
We corrected the data by unchecking it and this got your fill-up history back to normal, with reasonable MPG values showing up for fill-ups where you did fill you tank to full.
On those fill-ups where you got to full tank our system will calculate a total of miles driven from previous "to full tank" fill-up and divide it by total number of gallons used to drive that distance.
If you mouse-over the MPG values our system will display a helpful hint as to how it calculated that MPG value. That hint is usually helpful for troubleshooting issues like this one.

Please let us know if you have any other questions or comments.
Thanks and have a great day!

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#8 2008-10-13 02:45:24

tankbeans
New member
Registered: 2008-02-28
Posts: 7

Re: MPG calculation flawed

I'm curious. I have my account set to calculate using American gallons as a system of measurement, but when I go to User's Top MPGs it is listed in imperial gallons, which I gather are larger than American gallons.

Is this straight across the board so people can see where they stack up, apples to apples, instead of apples to oranges? Does the site do the same thing for people who are doing km/gallon or whatever other system there is?

Thanks.

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#9 2008-10-13 10:20:15

support team
Administrator
Registered: 2007-06-20
Posts: 188

Re: MPG calculation flawed

Dear tankbeans,

That page is using "display metrics" other than user account metrics to display MPG values. To change your display metrics please click on the US flag at the top right corner of our site. Probably a while ago you clicked on Great Britain's flag and our site remembered your preference.
Since this feature is causing some confusion we will add some code to reset "display metrics" to user account preference on login.

Please let us know if that answers your question.
Thanks and have a great week!

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