The Course Was Long!
Your GPS isn't always right.
Your friend has just run the Shamrock’n Half Marathon and you ask her how it went. “I was a few minutes slower than I was hoping,” she says. “But the course was a little long. My Garmin shows 13.3 miles so if I take off that extra two-tenths of a mile, I’m exactly where I should be.”
This, of course, is nonsense. Every race, and every race day, has its own idiosyncrasies. While your GPS watch may be a wonderful training tool, and amazingly accurate, what it shows during a race cannot be used to check the accuracy of the course measurement.
Although it will happen occasionally that a course is measured inaccurately, or marked incorrectly on race day, most are remarkably close to their specified distance.