I swear-I can drive to my office 4.5 miles at 30 MPH for 3 days straight, then take a road trip on the highway for 350 miles at 80 MPH and my computer "average speed" stays right around 31 MPH. Is this normal? How often does the computer recaluculate? Seems mine never reads more than 31 MPH regardless of city or highway driving. My gas mielage as well. Thoughts?