Difference between apple watch series 8 & 9

- Difference between apple watch series 8 vs 9
- Difference between apple watch series 7 8 9
- Main difference between apple watch series 8 and 9
- What's the difference between apple watch series 8 vs 9
- Difference apple watch series 8 et 9
- Difference apple watch series 8 vs 9
- Difference between apple watch 7 and 8