In addition to weather monitoring, forecasting and early warning services, the Observatory is also an official timekeeper in Hong Kong. The time service is based on the caesium beam atomic clock. The latest generation of caesium beam atomic clocks is the product of 40 years of technological evolution, and has an accuracy within 0.01 millionths of a second per day. But just how accurate is the caesium beam atomic clock? How does it work?
40 Years of Caesium Beam Atomic Clock (in Chinese)
