Good dead tree MPG log?

[TonyPSchaefer]

I then used this column to calculate Lifetime mpg since Tony's sheet assumes relatively stable "tank miles" values. (And has shorted his lifetime MPG slightly).

I don't get it, Bruce. What do you mean by "Relatively stable tank miles"? I'm not trying to call you out or be tricky, just admitting that I probably have an error in my spreadsheet and am welcome to an explination of what it is and how I can make it better reflect reality.

I reset my MPG every time I refill. Then populate my spreadsheet with this this data:[list]

I figured this was a sound way to do it. But if you can show me how to improve my lifetime MPG just by reworking some calcualtions, then call me Enron and let's fix some numbers!

[bruceha_2000]

Tony, I'm not saying you have an error in your calcs, just that it isn't as accurate as it can be. You'll note that you had only 279.40 miles on your first tank, the others were 420 miles and up. Since you average the tank MPG column to get lifetime MPG, each value is weighted equally but you actually had 188 fewer miles at 44.60 mpg on your first tank than 50.4 mpg on the second. Thus, your lifetime MPG after the second tank was actually 48.06 rather than 47.50. By dividing the total miles driven by the total (calculated) gallons, you avoid the inherent 'weighting' slop that happens when averaging averages.

Unless a person really varies how many gallons they put in every tank, I doubt the difference will amount to much of anything over time. In fact, the 'more precise' calculation yields a lifetime MPG of 47.34 vs your result of 47.23.

Now, where is that guy who was whining about us obsessing about getting max mpg :-)

[TonyPSchaefer]

Oh I see. Thanks for the explination.
I will replace the Lifetime MPG calcualtion with one that uses the Total Miles and the Total Gallons.

[gturtle]

Last time I filled up was a 500 mile tank. I was really pushing it, I drove more than 40 miles on a flashing bar. Towards the 500 mile point I was looking ahead for gas stations using guidance, since I was on unfamilar ground. At first I got just over 11 gallons in the tank, then I noticed that I got exactly $25 dollars in the tank. I realized that there was some confusion over how much gas I wanted to buy, I had only paid for $25. Since I wanted to see how empty the tank was I swiped my card again and got a total of 12.6 in the tank, but it sloshed over even though I wasn't holding the nozzle. So now at 130 miles on the new tank I still have all the bars, even though my MPG has sucked due to a short commute recently.

The gas was something like $2.25, the most I have ever paid. Gas prices have really spiked here in Southern California in the last couple of weeks, from just under $2 to roughly $2.20.

Back on topic, it made a complicated entry in my log! Right up there with the one where I ran out of gas in Nevada, when I had to note the rescue gas and then the fill.

[TonyPSchaefer]

Having looked at John1701a's website, I have decided to add average temperature to my spreadsheet and graph. I plan to plot it on the secondary axis in bars counter to the MPGs being plotted in lines. I think it will make a nice comparison showing how temperature affects MPG.

But what are your thoughts on how to calcualte average temp? I found that weather.com provides daily highs and lows for the previou 45 days or so. Is it mathematically sound to figure the average temperature for the day by averaging the day's high and low temperature? I figure probably not, but honestly, it's not really worth it for me to note the temperature at every hour and create an average that way. I also don't plan on noting the temperatures everytime I drive Priapus, even though that would probably provide the truest results.

What are yout thoughts?

[tms13]

My version supports partial fills, and does the calculations only when you fill to the top again; it also accepts the date, and calculates monthly averages when appropriate.

My strategy for temperatures is to note the max and min temperatures when I'm driving - being out by even 5°C isn't that big a deal for me, really. I don't know yet how much correlation I'll see.

I've attempted to save it into Microsoft format to attach; no idea if that actually works! If it has, you'll see yellow fields which are where to enter data; the interesting (calculated) stuff appears to the right of it. I've even populated it with some data that I made up (okay, I'm lazy, and I used my real data). It would need a bit of adaptation to work in US units, but the principles show carry reasonably well.

To date, the only part-fill I have is 0.0 litres - this was because the current MPG got reset whilst fitting my stereo. But in normal running, a handful of times a year I end up having to fill somewhere expensive, and put in just enough to get me somewhere more reasonably-priced.

If you want to see how it all works, you'll want to unhide columns J-R.

[bruceha_2000]

Tony, for your personal use, Toby's "avg temp while I was driving" is the most accurate. You would have to write down the temps from your MFD. Lot of work if you do many trips throughout the day and night though.

Avg for the day from the newspaper would at least give you a general correlation of MPG and temp. Averaging the avg daily temps wouldn't have the same precision loss as your original lifetime mpg becuase there are always 24 hours in a day.

[TonyPSchaefer]

Holy Crap, Toby! I'm really hoping that layout evolved over time. There way too much there to think that you sat down one day and just laid it out. It's extremely thorough. Moreso than I'm really interested in. Very impressive.

[tms13]

<div class='quotetop'>QUOTE(TonyPSchaefer\";p=\"45017)</div>

Holy Crap, Toby!  I'm really hoping that layout evolved over time.  There way too much there to think that you sat down one day and just laid it out.  It's extremely thorough.  Moreso than I'm really interested in.  Very impressive.[/b]

Don't worry, it did evolve over time, though I spent a couple of weeks deciding what I would be interested in. Reading the Fuel Economy board here added some things so I could convert to US units for comparison with other members, for instance.

The monthly calculations are pretty much a copy of the tank calculations, just with a different trigger to say it's time to do the adding up - change of month rather than a complete fill.

I hadn't done much spreadsheet stuff, so doing this was also a good way of learning to use OpenOffice. Not sure I've really got the hang of the chart stuff yet, mind.