https://www.youtube.com/watch?v=MHOTAhHjtww
Salisbury Cathedral clock
https://www.youtube.com/watch?v=Wu2C-XDdywM
https://www.youtube.com/watch?v=KbJb92H5gy8
Early clocks
Mechanical clock
https://youtu.be/ynkh4Hwf9ik?t=16m31s
A Brief History of Timekeeping
https://www.youtube.com/watch?v=URK9Z2G71j8
