Nike+ iPod imprecision

I have been running off-and-on for the last 3 years (mostly off) and running regularly for the past 15 months. I love how lightweight it is the antithesis of biking or backcountry hiking with their emphasis on gear. Running is nearly completely free of equipment and gear. All I do is strap on my shoes, plug in the headphones and go. The exception to this is my Nike+ iPod pedometer. This is a cool gadget that consists of a sensor which goes in your shoe and a receiver which plugs into the 30-pin connector on the bottom of the iPod Nano. If you use an iPod Touch you don’t even need the receiver.

I was blown away by the accuracy of the device and have been rediculously satisfied with this $30 gadget. Two events brought home how accurate the pedometer was: I ran a Cinco de Mayo 5k in Brooklyn with my sister a few years ago. The pedometer signaled 5k on the very footfall that crossed the line finishline. It was accurate to the step. Amazing:

I had a similar experience in the Detroit Marathon Relay in 2007. I ran a short segment from Downtown to Belle Isle. As soon as I crossed the timing blocks the iPod signaled I had reached my goal:

Last fall when I did the half marathon the accuracy fell a bit. It recorded 13.6 for a 13.1 mile route but I felt that 5% slosh was okay:

I had the same over estimate occur during the martian Marathon 10k. With the devic recording 6.5 miles for a 6.2 mile run. Again a 5% error:

What inspired this post was the new finding that in 2009 the error has swung in the opposite direction, now the Nike+ is underestimating my distance and speed. I first noted this during an 8.5 mile loop I ran with PBFluids reader and fellow nephrologist Steve Rankin. The Nike+ only recorded 7.98 miles:

Yesterday I did the Dexter-Ann Arbor half marathon and again the Nike+ iPod underestimated the distance and speed:

In the end it was only off by 0.6 miles over 13.1, so 5% but on my next run my Nike+ odometer will cross 1000 miles and its a little less satisfying thinking that I already crossed that milestone at some unrecognized time in the last month or so.

Update: Just discovered that the New York Times recently did a review of the Nike+iPod system.