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rsdavis9 04-21-2013 01:41 AM

avg mpg calculation
I have entered 7 fuelups for my tdi diesel. I displayed total gallons used and calculated the mpg. 2553/81.02=31.5. I am using odometer so I subtracted the first fuelup 15.56=65.46. 2553/65.46=39.000. I still see an avg mpg of 55. How do you calculate the mpg? I know it will get better with more fuelups but I would like to know how you calculate it.


dtwjr 04-21-2013 02:34 AM

I only use trip miles to calculate MPG. Gallons used divided into miles driven gets it every time (example: 260.6 miles/7.43 gallons = 35.1 MPG). I don't find odometer readings useful for tracking MPG, although it is useful for other things like service intervals.

rsdavis9 04-21-2013 04:52 AM

odometer works fine because the trip = odo - prev odo.

What I don't get is how to start it off. The other advantage of odo is cant screw up by forgetting to zero or accidentally zeroing.

rsdavis9 04-22-2013 12:03 AM

I figured out how you calculate average. Basically you total all fuelup gallons except the first one and divide that into total miles tracked. The problem I was having is that you exclude other fuelups. If you mark partial you exclude those gallons and the next one after the partial(s). This is fine except for the fact if you use odometer then the miles of the partials still get included. I can envision a better algorithm(see below). Also anytime a fuelup has zero miles or other nonsensical numbers you also exclude that fuelup from the totals. The better algorithm is that if you mark partial still include the gallons but don't show the avg until you come to the next fuelup which isn't partial.

waterboysh 04-22-2013 06:22 AM

Partials should be calculated into the average as long as there is a total fill up some time after them. You will know what the average mpg is over the course of several partials because you still know the total number of gallons used and the total number of miles drive. You just wont be able to get mpg stats for the particular fillup if it's a partial because fuelly has no way of knowing how much gas you used, at least not until you fill it back up all the way.

rsdavis9 04-22-2013 10:19 PM

Yes that is the way it "should" work. But in my experimentation it doesn't work that way with odometer tracking.

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