Innacurate distance measurnments - two different Runner 3 watches

EddieF Registered Users Posts: 1
New Seeker
edited January 24 in TomTom Sports
Me and my partner were recently running the Barcelona marathon, both with Runner 3 watches. Throughout the run almost immediately our watches did not match the distance signs of the marathon, and over the entire run we accumulated on both watches 1.2 (!!!) km more than the actual distance. What kind of accuracy is that?!

Did any one experienced similar thing? How did you resolve it?
Any response from TomTom representatives?

BTW needless to say that the night before we have synchronized both our watches for updating the quickGPS.


  • tfarabaugh
    tfarabaugh Posts: 16,941
    That is actually quite normal. The nature of GPS is that each data point collected is only accurate to within 15-30m of your actual location. The watch collects the data points and then tries to figure out a route using them (considering that some points may overlap or duplicate). The website then smooths the data to come up with the most reasonable route taken according to the algorithm it is programmed with. Every watch, even two of the same model, will come up with different distances, as they are collecting different GPS data. Even on a certified course the distance is a best-case scenario running 18 inches from the curb, not going around anything (water tables, police cars, other runners) and taking all tangents. In addition, measured courses add 1 meter per kilometer as a buffer so they are always a bit long and distance posted can be notoriously off. Even championship marathoners run loner than 26.2 miles in a race.