You can change which one you're showing by tapping on them when customizing the watch face — third - party apps can add their own complications as well. (digitaltrends.com)
The fingerprint sensor on the back can also be used to capture a selfie when tapped on it, after opening the camera application. (phoneradar.com)
The reason is, you can precisely aim for the enemies or objects you want by just tapping on them instead of using the right analog stick to try and hit it. (waytoomany.games)