How does your Apple Watch know when to tell you to breathe?

Related questions

1. Can Apple watch measure HRV?
2. Can fitbit measure heart rate variability?
3. Can Apple Watch Do HRV?
4. Does the Apple Watch tell you to breathe when you're stressed?
5. What is low heart rate variability?
6. What is a good resting heart rate by age?
7. Can your HRV be too high?
8. Is 50 bpm too slow?
9. What does low HRV mean?
10. What is elite HRV?

Tags

1. #contract
2. #session
3. #apple
4. #graphics
5. #notifying
6. #screen
7. #feedback
8. #accompanied
9. #breathe
10. #begin
11. #breathing
12. #haptic
13. #watch
14. #ignore
15. #circles
16. #display
17. #simply
18. #either
19. #reminder
20. #exhaling