I was programming Tess's navigation to take my wife from Napa to the Sacramento airport. It routed her over the back hills through Winters for a trip of 62 miles. When I do the same using Google Earth on my computer it routes you up I-80 to Davis, then north to Woodland for a total of 69 miles. The latter route is what we have always used, as you are at freeway speed for the entire trip. The former trip is mostly windy 2 lane roads. I am deducing that the navigation system simply computes the shortest route in miles, with no regard to speed. Is this documented anywhere? Would be nice to have the option, as most GPS systems do, for shortest, or fastest.