In addition to providing notifications, the Apple Watch is also supposed to be a powerful fitness and health gadget designed to both motivate you and record a variety of parameters related to your daily activities and workout sessions. One of the things the Watch can record is your heart rate, and Apple has put together a special page on its support website that details how the sensor on the back of the Watch works and how to get better results from it.
How to make sure one of Apple Watch’s key health features works