## Friday, November 07, 2014

### shortchanged!

I finally did an experiment to see whether my pedometer has been shortchanging me in its measurement of distance. As I'd mentioned before, I knew that I walked at a speed of 3.2 miles per hour after having taken careful measurements while back in the States. The local bike path that runs along the George Washington Parkway has markers placed precisely at every mile; those markers, coupled with the Google Earth ruler (which can measure distance down to the inch), are what led me to the 3.2 mph figure. So I reset my pedometer to show kilometers, then took a lap around our campus's 400-meter track. Sure enough: the pedometer, that stingy bastard, registered only 300 meters of travel. Since I don't know exactly how the pedometer reckons distances, I don't know whether that's exactly 300 meters, or something more like 325, 350, or 375 meters. (The pedometer shows one decimal place when measuring kilometers; when I started walking that day, the pedometer read "4.0 km"; after one lap, it read "4.3 km.")

Conclusion: I may have to multiply my registered distance by 1.06 or 1.33 to get a more accurate notion of my true distance traveled. The average of 1.06 and 1.33 is approximately 1.2, so that'll be my multiplier from now on. Henceforth, whenever I report distances traveled, you can assume I've multiplied my pedometer's figure by 1.2.

Ken Cooper, who wrote the 1970s classic Aerobics, notes that if you walk down the same path that you walk up, the difficulty of the up-slope and the ease of the down-slope cancel each other out. I'm going to assume that the same goes for speed: I'll walk slower than 3.2 mph uphill, but faster than 3.2 mph downhill. The overall average will therefore be 3.2 mph.

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