It's interesting to noodle the graph...
But I'm not sure using
average speed as a measurement over an entire tank works well as feedback to the driver
unless the tank is predominantly highway/rural cruising, and other tanks results are over the same/similar route. (IE - controlling for as many variables as possible.)
EG: if a tank includes a siginificant mix of city/suburban plus highway motoring, how do you interpret the results & use the average speed number to your benefit?
Also: does the measurement of average speed include time stopped? (EG: the
ScanGauge average speed calculation is not a "rolling" average, which would be more useful. Its calculation includes time stopped.
Consider too that spread out through the year, weather effects will affect the MPG numbers (cold weather = worse mileage; warm = better). How is that separated from the average speed variable?