shimano flight deck average speed calculations
 

Does anyone know how the flight deck computes the average speed?

After reseting the trip timer, which resets the average speed, I get "off results":

trip time: 1 hour
trip distance: 17.5 miles
average speed: 15.5 mph

trip time: 2.5 hours
trip distance: 40 miles
average speed: 16.5 mph

Both of these are off, one high, one low. Thoughts? Am I missing something mathematically basic?

Don't know for sure, but it looks to me like the Flight Deck doesn't count time for average speed when the wheel isn't turning. See how it compares with the elapsed time readout.

Not sure how it works, but what I can tell you is that my new Polar 725 agrees with my Flight Deck on the same bike.