Disappearing Distance

Smashbox

My watch is not accurately calculating the distance I have run. It always shows a shorter distance. Today I ran 20km, it showed 18.7. The greater the distance, the more kays I am short.

tfarabaugh

How do you know you ran 20km? What were you using to judge this, how do you know it is the watch that is wrong?

Smashbox

I measured the distance in my car. Also, when I run with others they always run further according to their watches.

tfarabaugh

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 smooths 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. You are assuming your friend's watches are any more accurate than yours or that your car is properly calibrated. In addition, you are not running the same line as your car, you are taking corners tighter and are likely on the opposite side of the street. all the small changes add up. In my experience the TomTom is among the most accurate watches on the market. Garmins, on the other hand, seem to consistently measure long. 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.

Smashbox

Thank you for your help! It just still seems that 1.5km is a lot to be “missing “.

Smashbox

if you don’t mind, may I ask if pausing my watch during water breaks could affect the accuracy?

tfarabaugh

Smashbox wrote:

if you don’t mind, may I ask if pausing my watch during water breaks could affect the accuracy?

As long as you are not moving it should not impact it. lf you move a distance and then restart it it will connect the dots from the pause point and the restart point.

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.