With the use of the built-in accelerometer in the new Forerunner 220 and Forerunner 620, questions have come up about how it works and how accurate is it.
These watches use a three-dimensional accelerometer which measures movement in all three dimensions, just like our foot pod. This is not to be confused or compared with a pedometer which just measures one dimension (or basically just counts steps).
There is no manual calibration for this. Every time you run outdoors with GPS, the accelerometer gets calibrated to your running style. Basically, a table is created on the watch for many different paces, so the more you run outdoors with GPS and at different paces, the more accurate it will be when you run without GPS. If you have never run outdoors with GPS under 9-minute miles and then run on a treadmill at 7-minute miles, your accuracy will not be as good.
Because a person's arm swing is not as consistent as their foot strike (you can't skip a foot strike but you can miss an arm swing by drinking, scratching, giving the #1 sign to the driver that cut you off), you should generally see greater accuracy with a foot pod.
The accuracy of the different ways to generate speed and distance in order typically are:
- GPS (typically well over 99% accurate)
- Foot Pod (typically around 98%)
- Wrist-worn accelerometer (typically about 97%)
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