How does Google Analytics calculate average time on page?

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Tags

1. #single
2. #difference
3. #viewing
4. #google
5. #users
6. #average
7. #between
8. #visit
9. #simply
10. #analytics
11. #measuring
12. #after
13. #amount
14. #recorded
15. #visitor
16. #tracks
17. #leaves
18. #bounce
19. #spend
20. #timestamps