Book 28, Question 105
How does a fitness watch count your steps?
A fitness watch has a tiny sensor called an accelerometer, which notices every time your wrist speeds up or slows down.
Each step makes a regular bump in the motion. The watch’s software counts these bumps and turns them into steps. It also guesses the length of your stride to estimate distance. Outdoors, many watches add signals from GPS satellites for a better measurement of where you ran.