Newsflash: your GPS watch isn't perfect. It is a series of points connected by ... blah blah blah ... certified races are just that - certified - through super fancy means of measuring ... blah blah blah.
Shelby at Eat, Drink, Run does a much better job explaining why the course is not long and your GPS watch is not perfect. With some pretty sweet MS Paint illustrations.
And in totally related news, guess what was delivered today?
I opened the box and LOLed. April 21 is my wedding anniversary. HOW DID GARMIN KNOW? It's also my Dad's (and his twin sister / my aunt's) birthday.
Anyway so now I can start plotting my shorter-than-Garmin-says runs. Although I'm sure the free apps on my phone have been doing a stellar job for me so far. Which for the record, said the Soldier Field 10 Mile was 10.15 miles.