Apple wants the fitness tracking abilities on your Apple Watch to be even more precise. The company has been granted a patent (9,459,118) for “adjusting step count to compensate for arm swing.”

According to the patent, a mobile device can receive a motion signal from a motion sensor on the mobile device. The device can determine a step count based on the motion signal. The Apple Watch can transform the motion signal from a time domain signal into a frequency domain signal.
The smartwatch can determine a dominant peak and harmonic peaks of the motion signal within a pedestrian frequency band. It can determine that the dominant peak corresponds to an arm swing of a user and adjust the step count to compensate for the arm swing.
Of course, Apple files for — and is granted — lots of patents by the U.S. Patent & Trademark Office. Many are for inventions that never see the light of day. However, you never can tell which ones will materialize in a real product.
