(Answer is none.) Here's the story. Today was a beautiful day. 70F and sunshine.
I just ran the Charles River loop between the Museum of Science and River St bridges fully instrumented.
Full image here This is the route recorded by my Garmin Etrex Vista Cx in my back pocket. I also had my Apple iPod Nano with the Nike+ kit.
The Nano computes speed/distance by measuring foot strike time. It overestimates my distance by about 5% usually. But I don't bother to recalibrate it because it would depend on the running surface: treadmill, grass, hard mud, gravel, tarmac, concrete all affect the foot strike time differently. Clearly, there are some issues with the GPS data points recorded. I'm pretty sure I can't run at nearly 30 mph. Zooming in at the Museum of Science reveals some oddities:
According to the tracklog, I've been doing some impossible zipping around. Of course, we need to delete those outlier points. Google Earth then reports:
The Nike+ kit doesn't record every footfall. It saves a reading every 2 seconds and performs lots of smoothing:
Finally, there is a well-known reference guide to this course (probably obtained by someone with a measuring wheel):
Summarizing, we have:
|iPod Nano Nike+||8.13|
|My best estimate||7.6|