In ODO mode, the average display includes all time since you last re-set. To re-set, open the info display and navigate to the fuel history screen. There you can reset the current memory, or erase all memory. It holds 6 resets, represented by the vertical bars. I reset this at every fill-up. Of course you also have 2 trip meters which can be used in the same way. The average MPG display relates to the trip meter you have showing.
Since I've adopted the habit of pumping gas until it clicks off, the trip computer mileage is extremely close to the manual calcs.
