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.

Notes on the Amica Insurance Iron Horse Half Marathon course:  The most common cause of indicated long courses is that the runner didn't run the shortest route that was measured. The Iron Horse course has quite a few winding sections that were probably not run along the same line that was measured. The Short Course Prevention Factor is 0.1% or only about 69-ft 3-in for a half marathon. Due to feedback after the 2009 Amica Insurance Iron Horse Half Marathon, the certifier made two independent rides of the course to validate the measurements. The measurements resulted in a difference of only 2-ft 2-in. This is well within the USATF requirement of 0.08% and indicates that the two rides were accurate, certainly not 0.2 miles different.