See also:

• Business: Business Services: Supplies and Equipment: Time Recording and Management  (95)
• Computers: Software: Accounting: Time Tracking  (112)
• Computers: Software: Human Resources: Time Keeping Systems  (57)
• Science: Astronomy: Calendars and Timekeeping  (55)

Cesium Atomic Clocks: - Kinds of cesium clocks, with pictures, plus a description of their operation and the science behind them.

Doug's Atomic Clocks: - Details on Doug Hogarth's experiments with his atomic clock.

How Stuff Works: Atomic Clock: - Concise history, background, definitions and operational information regarding atomic clocks.

How Stuff Works: Pendulum Clock: - Concise description using drawings and animation to show the operation of a pendulum clock.

Smithsonian Institute - On Time: - History of the clock and how Americans have measured time and been affected by it.