Apple's best-selling smartwatch can keep watch over your heart rate, take an instant ECG from your wrist and, most recently with Apple Watch 6, show how much oxygen is in your blood. As well as monitoring those vital statistics, you can also track your daily exercise routines such as runs, walks and swims along with making sure you stand up enough each day. It's all clever stuff, but if you've recently joined the wearable revolution you might not be aware of a few extra health features hidden inside the Apple Watch that can really help you achieve your goals. Here are three of our favourites...