See also:

• Business: Business Services: Supplies and Equipment: Time Recording and Management  (106)
• Computers: Software: Accounting: Time Tracking  (127)
• Computers: Software: Human Resources: Time Keeping Systems  (85)
• Reference: Time: Current Time  (32)
• Reference: Time: Horology  (30)
• Science: Astronomy: Amateur: Sky Calendars  (14)

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.