Button 1 (swipe up on Bangle.js 2) resets all measurements except total distance traveled. The latter gets preserved by being written to storage every 0.1 miles and upon exiting the app.
If the watch app has not received an update from the sensor for at least 10 seconds, pushing button 3 (swipe down on Bangle.js 2) will attempt to reconnect to the sensor.
Button 2 (tap on Bangle.js 2) switches between the display for cycling speed and cadence.