me and my co-worker were discussing commutes when I tried to compute his cost per trip down to +- 10 cents. This kind of computing is really hard to do in the head so my idea is place your make model and it would give your mpg's, punch in cost per gallon and finally how many miles was your trip (alternatively you could press start when trip begins and stop when finished and gps would give precise distance, therefore you would get exact cost of daily commute.