But my GPS says......

Sunday's Citizen's Bank Caesar Rodney Half Marathon / 5k brought record crowds to downtown Wilmington. At the start it was 54 degrees with sunshine. With 1500 finishers in the half and another 208 in the 5k this years CR was our largest ever. A bit surprising with the winter weather we had here in Delaware. How do you run outside with 56" of snow on the ground? On the Friday afternoon before race day I rode the route with Jon Clifton. Jon was with me to chalk out the course since I am still recovering from hip replacement surgery. I had with me Doug White's USATF certification papers #DE07014LMB.
Doug marks the start, finish, and mile marks with white paint. Each mark has a description of where each marking is located. An example is 13' south of telephone pole 22856-2467 which includes a drawing of this location. When chalking out a route I always carry a fresh can of white spray paint. Why? So i can re mark all of the markings from what Doug has done. This makes it much easier to find year after year. The day after the race I received an email from a runner asking me if the course is certified. I emailed back "yes" and provided the certification number. He replied, "my GPS watch says the route was 13.3 miles." I called Doug White who ran in the race and asked him about this. His comment was, "if the GPS watch is so exact why do they use a Jones counter to certify race routes." Doug stated that we ran the exact route and his splits were right on. As race director I am a stickler for accuracy. 2/10 of a mile off is a huge amount of distance and is something I can't believe is true. For those of you wearing GPS watches.......have you had issues with routes that advertise certified only to find them not accurate according to your GPS? Just curious.