When charging, you see 1 to 5 blinking lights. Each light means 20%. This is showing 2 lights at 40% charged.
This is showing fully charged with 5 lights at 100% charged.
Double tapping shows your progress for the day. This is showing 1 light at 20% towards the goal. Five lights would mean the goal is reached.
After double tapping, If all 5 lights are steady, this means you've met your daily goal.
Tapping multiple times will put it in sleep tracking. Then 2 lights will shine then fade away indicating sleep tracking is on.
Double tapping while in sleep mode will show the 2 jumpy lights to confirm it's still sleep tracking.
Tapping quickly multiple times while sleep tracking will take it out of sleep tracking. All lights will blink together and then scroll back and forth.
Now that sleep tracking is off, double tapping will now show your progress for the day.
When not in sleep mode, if you tap to check progress and all you see are the two blinking lights instead of the progress lights, this indicates a low battery.
I hope you find this helpful. Nowhere on the web could I find a complete explanation of these lights.