Math error with the running average - Fuelly Forums

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Old 06-25-2011, 04:28 PM   #1
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Math error with the running average

Is there a math error with the running average? I understand that it uses the last 10 fill ups, but I have 8 fill ups total (all since April) and my running average is 20.1, but my regular average is 20.3

What happened to the other 0.2 MPG?
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Old 06-26-2011, 01:32 AM   #2
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The two stats use slightly different methods of calculation. The running average takes all of the averages that have been calculated for your fuel-ups so far and averages them. Your total average on your vehicle profile page takes total miles / total gallons to reach that figure.

We've found that for your total average, using this method of calculation is slightly more accurate because it includes partial fuel-ups. However, for short time periods, using the average of calculated averages tends to work out better specifically because it doesn't include partial tanks.

So it looks confusing in your situation since the two should match, but the different methods of calculating things lead to different results. And we try to use best method of calculating for the type of stat.
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Old 06-26-2011, 09:07 AM   #3
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Ahh, ok. I got it.

I did the math by hand for the "average" average and got basically the same thing. 20.06 rounded up to 20.1 (160.48 total MPG averages / 8 fill ups) vs my 2092.2 miles / 102.98 gallons for 20.31 rounded down to 20.3.

So, if I have this right, regular MPG average is all fillups, running MPG average is average MPG of last 10 fillups, except for partials, right?
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Old 06-26-2011, 11:35 AM   #4
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Yep, that's it—almost exactly. When you add a partial tank, Fuelly doesn't calculate an individual MPG for that tank or the next one. So even if that tank after a partial is full, it won't have a calculated MPG. That means it won't be included in the Running Average MPG on your dashboard.

So just to make it completely clear I'd say that running MPG average is the average MPG of the last 10 fuel-ups, excluding those without a calculated MPG.
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Old 12-20-2013, 11:45 PM   #5
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Is there a way to suppress running MPG as the primary reporting number. It is immaterial to me, I want only my average based on all gas and mileage. It is annoying that I have to click through to get this.
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