Apple Insider:

The U.S. Patent and Trademark Office on Thursday published an Apple patent application covering a smart wrist-mounted pedometer that can automatically determine its location on a user’s body and compensate for missed steps using advanced processing algorithms.

Since readings from on-board sensors reflect detected changes in magnitudes of forces, including gravity, software analysis now plays a large part in outputting accurate movement data. As far as the hardware is concerned, spikes in directional magnitude can be masked by arm swings, jolts of taking a step or a bump against a keyboard.

Further, current algorithms based on peak magnitude and step frequency data fail to sufficiently take into account possible missed steps. For example, some systems compare a moving average of magnitude measurement thresholds, a technique that can miss steps due to motion interference. This is especially problematic when a device is worn on the wrist as a user’s arm swings may offset or otherwise disrupt readings.

Bottom line, differentiating a step from, say, a bump or an arm raise is a difficult problem to solve. Arm biometrics is an important part of the future. This is just one step of many to come, I’m sure.