Faulty distance on TomTom sports watch?

ajg12358

A friend & I went for a run yesterday. At the end my Tom Tom showed 7.14 miles, but his (not a Tom Tom) showed 7.44. The times were just 6 seconds apart. Is this a GPS tracking problem? Is there any other explanation?

tfarabaugh

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 and different brands have different algorithms and methodology to smooth the data into a meaningful track. There is actually no way of knowing which device is correct without going out and manually measuring the course on the exact track you took using a measuring wheel. GPs is convenient, but consumer grade GPS is not exact. I would not assume that yours is wrong and his is right (and vice versa) as some brands are notoriously long (Garmin), while others are notoriously short (Suunto) in my experience. I find that the GPS accuracy for TomTom is about the most accurate I have found.

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.

ajg12358

Thank you very much for your reply and I understand what you say. I suppose the only thing that surprised me was the size of the difference between the two watches - an error of around 4% seems quite large. Still it's very good to hear that you've found Tom Tom one of the most accurate watches! Thanks again for taking the time to write in.