In a previous post (GPS Accuracy) I reported the discrepency between my GPS (which is a many-year-old Timex) and my running buddies (which was a Garmin Forerunner). Well, to revisit the issue, he got a new Forerunner. And as of last night's long run, they are still off -- a half mile over a 18 mile run. So something wierd is definately going on. His was the shorter distance.

So I plotted the run on MapMyRun.com and it comes to 18.53. My GPS showed 18.76, the Garmin showed 18.26. So, I'm no nearer to the answer. I'm guessing that the Garmin is losing the signal a little more often and so isn't getting all of the twists and turns? And Mine is showing more because I'm not religious about mapping every turn and bend in MapMyRun? But those are guesses.