I've been tracking my mileage in Excel since I bought my car. For most of that time, I've also been resetting the average mpg and average speed on my trip computer at each fill-up. That way, I can tell what the difference is between the trip computer and actual, and see how much average speed influences mileage.
I would love to see how this compares to others with my model vehicle. Can those values be added as optional data to enter?