كيف تعمل الساعات؟؟

1- Timekeeping and clocks FAQs [Internet]. NIST. 2020 [cited 2019]. Available from: هنا
2- [Internet]. 2020 [cited 2019]. Available from: هنا
3- How clocks work (in 5 easy steps) [Internet]. The British Museum Blog. 2020 [cited 2019]. Available from: هنا