On the vehicle scale, I believe the individual records are broken into four equal sized groups. Then the vehicle averages use the center pair. Thus the best and worst vehicle records are dropped for the fleet average.

Within a single vehicle, it is possible to use either the individual calculated MPGs or the miles and gallons. So far, I've not found a significant difference with either method. In the case of the Prius, we know the tanks have a variable capacity. What this means is some tanks have excellent MPG and other are poor. However, the MPG averages over time seem to even out.

One last comment, MPG is not a competitive sport except within the performance of each vehicle. Improving my vehicle performance pays me a dividend. Being better or worse than another vehicle has no payback at all.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
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