Difference in distance on Spark

Heinzt

I do have distance difference of .250 miles between my watch and the mile marker when I run 1/2 marathons it does not change it is exact 1/4 mile ahead on each mile different any idea how to correct this issue ?

tfarabaugh

Is it off .25 every mile and adds up (so it is .5 miles ahead after 2, 1 mile ahead after 4, etc.) or is it just reading longer at the end? If the overall distance is off by .25 miles this is totally 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 watch then smoothes the data to come up with the most reasonable route taken according to the algorithm it is programmed with. This is why 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 and taking all tangents. In addition, measured courses add 1 meter per kilometer as a buffer so they are always a bit long. Even championship marathoners actually run longer than 26.2 miles in a race. Also, do not make the assumption that the race officials or the distances others get are correct any more than the distance your watch gets is. The race officials may have gotten the distance using a GPS device with the same accuracy issues (as opposed to certifying it using a wheel). In my experience the TomTom is among the most accurate watches on the market. Since GPS is really just an estimate, you ultimately have to pick a device you trust and stick with it.

I hope this helped answer your question. If so, please mark it as a solution so others can look for it if they have the same question.

Heinzt

I sure appreciate your information,my tom tom only shows .250 off at the complete 1/2 Marathon run so your explanation is right and verse explanatory thank you very much for your reply Heinrich

tfarabaugh

Heinzt wrote:

I sure appreciate your information,my tom tom only shows .250 off at the complete 1/2 Marathon run so your explanation is right and verse explanatory thank you very much for your reply Heinrich

I am glad I could help. When you get a chance please mark my response as a solution so others with the same question can look for it.