GPS Calibration: I wore a Garmin GPS watch during the Half Marathon and had a distance in excess of 13.31 miles. Why was the course a good 2 tenths of a mile longer?
All calibrated course are measured based on a required built-in safety factor which always results in a course which is slightly longer. Since we also measure the tangent to get the shortest route, a winding course would measure even longer based on the standard “side of the road” running of most runners. It is also possible that other changes in GPS connections can result in variations in the distance measured. Movement of the arm can also throw in a wrinkle. The calibrated process results in a course which is within feet of the expected distance which is always long due to the safety factor.
