What is the difference between Iwatch 3 and 4?

Related questions

1. Is the Iwatch 4 waterproof?
2. Can you FaceTime on Apple Watch Series 4?
3. Can I really swim with my Apple Watch?
4. Can Apple Watch do blood pressure?
5. Can you text on Apple Watch Series 4 GPS only?
6. Can you answer calls on Apple Watch?
7. Which Apple watch is waterproof?
8. Do you wear your Apple Watch to sleep?
9. Is Apple watch really waterproof?
10. Does Apple Watch 4 track steps?

Tags

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2. #including
3. #upgraded
4. #claimed
5. #sensor
6. #hardware
7. #features
8. #altimeter
9. #extras
10. #built
11. #processor
12. #optical
13. #faster
14. #heart
15. #watch
16. #barometric
17. #called
18. #apple
19. #series