I think it all averages over the long haul. I think the important thing is recording every fill with out skips and not just the ones with more than a set amount of gallons. The goal is to keep increasing and listing all tanks will give you a better trend. When looking at it you can always throw out the abnormal fills.
I have a big discrepency between a couple of fills because I didn't totally fill once so it looks like my mileage spiked but the average of the next fillup to the top and it brought it right in line with prior and subsequent tanks so put them all in and the graph shows the reality of them all.
i think only the 10 cars with the most gas logs should be used, each with different colors and plotted with gallons at the x coordinates and mpg at the y coordinates.
i predict we will see some interesting trends. obviously the further to the right you go the more gallons and thus the standard deviation of mpg will decrease making the readings narrow for each car. the standard deviation will probably increase exponentially as the fillup decreases.
however, i also anticipate, with the increase in standard deviation, an increase in the average mpg simply due to evaporation within the tank and probably a few other explanations to which i am not sure.
i expect the changes in these statistics to be fairly minor. also there is no need to do any data gathering. its all sitting in the usergarages ready to be plotted.
when i originally mentioned this to matt i was reffering to the difference in mpg between filling at a half tank, to 5/8, 3/4, 7/8, and limping to the pump with a tablespoon of gas.
don't waste your time or time will waste you
All I did was graphically point out that if you report a FE figure on a dinky fill-up it is likely to have a relatively large error in it- SO WHY BOTHER???
As previously noted, with enough data points the average will eventually bring things back in line BUT IF WE ARE GOING TO LOOK AT INDIVIDUAL FILL-UPS FOR ANY REASON WE SHOULD TRY TO DO THEM WITH THE GREATEST AMOUNT OF GAS WE CAN.
I understand your point there. i just overreacted a tad. is 8 gallons a dinky fillup? that what i usualy put in. it's nice only driving 10 miles a day to work!