MPG - mfd vs spreadsheet

[Cacti]

Originally Posted by qbee42

Not bad. I assume the spreadsheet fuel data comes from the pump readings? For those doing manual calculations, keep in mind that gas pumps are not 100% accurate. Typically they are allowed some set amount of error. You can guess which way the error usually falls.

Tom

Yes, the spreadsheet fuel data was from the pump readings.

[richard schumacher]

Originally Posted by sorthund

So should we still hit the reset button after refill?

It depends on what you want to see. If you want fresh MPG figures as you drive from that point, then yes. If you want the MFD to report net MPGs since the last time it was reset, then no.

[sleonardelli]

Okay, I've taken Jimbok's calculation and have come up with the following:

http://priuschat.com/forums/attachme...1&d=1214259777

Did I do this right?

[JimboK]

Originally Posted by sleonardelli

Okay, I've taken Jimbok's calculation and have come up with the following:

http://priuschat.com/forums/attachment.php?attachmentid=10097&stc=1&d=12142597 77

Did I do this right?

Hmm, not sure what you've done with that last column.

Let's assume you have columns A through G there and your headings are in row 1. Replace what you have in cell G2 and below with a formula that figures the difference between columns E and F:

[EDIT/CORRECTION]
A big brain f**t here. Forget this:

=F2-E2

and use this, formatted as a percentage:

=F2-E2/E2

[EDIT COMPLETE ]

Now in cell H2 and below use my formula but change the reference to column F (where I figure the difference between the two methods) to column G:

=(G2*(C2/AVERAGE(C:C)))

Format that as a percentage. That gives a "weighted difference" for each tank, weighted by how many miles were driven. Finally in cell I2 use this, also formatted as a percentage, to figure the cumulative difference:

=AVERAGE(H:H)

I didn't take time to transpose your numbers and calculate a cumulative difference, but the tank-to-tank differences appear well within reason. Your last tank's difference is greater than the rest, but with the Prius' flexible fuel bladder you can expect that sometimes -- see my two April fillups below. That's why you can't rely on calculated MPG for just one tank; the more you have, the more accurate it becomes.

To reassure you that you're in the ballpark with your tank-to-tank differences, here is my spreadsheet beginning last October when I first started tracking mine:

[sleonardelli]

Okay, tried but it's not working. Tried rearranging columns and its not working. I thought I knew excel pretty well but am just getting frustrated. I'm wanna try to attach my spreadsheet so you can see my calculations but PC doesn't allow for .xls.

BTW, started using your hypermiling technique (on YouTube) and have my highest MFD to date: 46!!!!!

[JimboK]

Originally Posted by sleonardelli

Okay, tried but it's not working. Tried rearranging columns and its not working. I thought I knew excel pretty well but am just getting frustrated. I'm wanna try to attach my spreadsheet so you can see my calculations but PC doesn't allow for .xls.

BTW, started using your hypermiling technique (on YouTube) and have my highest MFD to date: 46!!!!!

Send me your e-mail by PM and I'll be glad to send you my file. And congrats on the results!

[bushface]

the only MPG i trust is the life time mileage divided by total purchased. 8200 miles / 164.565 gallons = 49.8 MPG.

[mcsenerd]

Originally Posted by bushface

the only MPG i trust is the life time mileage divided by total purchased. 8200 miles / 164.565 gallons = 49.8 MPG.

I second this notion...

[JimboK]

Originally Posted by bushface

the only MPG i trust is the life time mileage divided by total purchased. 8200 miles / 164.565 gallons = 49.8 MPG.

No question that's the most accurate method. But that won't help much for results from individual tanks, nor will it tell me how far off the MFD is from actual. That's why I use the spreadsheet. Now with several months' data, I trust the MFD's results to be within a 2-3% margin of error.