When running with my Garmin Forerunner, I am often asked about the accuracy of GPS watches. I wondered this same question before buying my first Garmin, especially when comparing purchasing a GPS watch, footpod, Nike+ sensor, etc.  There are so many products that are on the market to track your distance and speed.

I have found that the most accurate product for me has been a GPS watch.  I tried everything that I could think of to test its accuracy when I bought my first Forerunner 305.  It faired incredibly well through each of my little tests.

After the watch locates satellites, you can navigate to a screen that shows you exactly how many satellites have been found and will tell you a margin of accuracy. Usually, when I check this screen I have found that it says that it knows where I am within 20-30 ft. This is the difference of only a couple seconds over the course of a mile. I’ll take that as being pretty accurate.

When I showed my sister all the things that my Forerunner could do, she immediately ran out and bought one as well.  We decided to go for a run both of us wearing the watches.  If the Forerunner is accurate, when we finish our 15 mile run, they should both say the same exact distance.  At the end of the run, we found that the watches had less of a tenth mile difference between hers and mine.  This small discrepancy is insignificant over the course of 15 miles.

I tested the watch with both driving a course that I ran to check it with my car’s odometer, measured courses on Google Earth (and other mapping software), ran the same loop over and over to see if the mile markers are in the same locations, etc.

It didn’t come easily, but I now fully trust my Garmin Forerunner.  I know on a 10 mile run that when the Garmin says 9.92, it means that I need to keep going because the Garmin doesn’t lie.