Bumping for the last bit of code.
Your methodology is not correct.
An average of an average gives you an unweighted average.
The average MPG is total gallons / total miles.
So it’s =if(B8=0,"",sum(c$2:C8)/B8)
:smack: D’OH!
OK, thanks for pointing out my error. Your formula didn’t quite work because it’s dividing the sum of gallons by the first distance, so I changed it to:
=IF(B2=0,“”,SUM(B$2:B2)/SUM(C$2:C2))
Now that the spreadsheet is sorted, there’s something I’ve noticed about the ‘new’ 2005 Prius compared to the first one: It does not achieve the efficiency of the old one. When I got the first one, I started out averaging (using the new formula) up to 48.8 MPG. There were some outliers in the beginning that looked a bit high. I try to refuel at the same gas station, using the same pump, and remove the nozzle as soon as it clicks off. That’s as close as I can get to reducing the number of variables, and the level at which the pump stops delivering fuel is not something I can control. I just reduce it as much as I can by using a certain pump whenever possible. Mileage is better in the late-Summer and Autumn than it is in Winter and Spring. Over five years my driving habits have changed. Since I’m driving less (telecommuting three days a week now), I can use a little more fuel and drive faster than I did in the beginning. Also, the SO is a bit of a lead-foot and she’s been driving my car. Recently, the car I wrecked averaged just under 46 MPG over the five years I had it.
The ‘new’ car is averaging just 42 MPG. This might be explained by the SO driving it, but even when I’m the only one driving it between fill-ups it’s only achieving 43 to 45 MPG.
I’m not sure why this should be. Seasonally, I should still be in the ‘higher-MPG season’. The old car and the new car are both 2005 models, and they both have all of the options. They should, for all intents and purposes, be identical – with the exception that the old car had over 237,000 miles on it, and the new one has about 116,000 miles on it now. It makes me wonder if the cars ‘learn’ driver behaviour over time, and the previous drivers didn’t care about mileage. (It was a corporate car, so the drivers probably weren’t buying the fuel.) But I’m not sure why a car would ‘learn’ this. That is, how could it do it? Why would it be designed to do it? My ‘it makes me wonder’ sounds like magical thinking. Without evidence, I have to reject that hypothesis and I’m left to wonder how an identical car being driven by the same people who drove the old car would get not-unsignificantly lower mileage.