How many times has somebody said "My official time was X, but my GARMIN measured the course as 13.3 miles, so my REAL TIME was Y."?
It's more than once, which is too many.
People: Your Garmin isn't perfect. It doesn't know where you are to within 1 centimeter at all times. It works off satellites. Which move. While you move.
Also, if you think the calorie count output gives you license to eat five desserts after your long run, think again.
I present: Lies my Garmin told me, just in one day (Saturday, at the Diamond in the Rough Tri):
And...no, Garmin, I was not below sea level during the run. Especially not 300 feet below sea level.