During my last trip to California I bought a Nike+ watch to record my runs. The watch (powered by TomTom) uses satellite navigation to calculate your position, so you can get all kinds of statistics about your runs. A cool gadget that worked flawlessly in the US, Germany and Luxembourg over the past 2 weeks. But not in China: when I did an outside run today and looked at the map of my run afterward I realized that the data are incorrect. This is the map of my run:
My start and end position are the same, but on the map they appear at different locations. That’s already an indication that something is not right. Next to that both the start and end position are in the wrong location, both are about 200-300 meters off the real place. During the run you can really see that the satellite data is manipulated, because I ran 4 loops of each about 900 meters (exactly the same loop 4 times in a row). The first one measured 800 meters, the second one 920, the third 850 and the fourth 880, too much of an error margin to be reasonable. When you look on the map you can see why: none of the 4 loops is in the same position! While running, the satellite changes the data it sends to my watch, meaning that you never know exactly where you are.
I re-checked my runs in Europe and the US and there is no error whatsoever. So it is China specific. This means the watch is not very useful here, at least not for precise measurements. I read before about GPS data from non-Chinese devices (=data from non-Chinese satellites) being slightly incorrect, but I did not realize how big the error is until I saw it myself. And worse, the error seems to change randomly over time.
Luckily I mainly run on my home treadmill when in Shanghai: air pollution is normally too bad to run outside, but today it was raining so I made an exception to run in the open air. So when I use my watch it’s normally outside China where it works well. But it still sucks that Big Brother is messing with satellite data. At least I now know it, so I won’t rely on my watch to tell me exactly where I am.