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.
Doug's Atomic Clocks
Details on Doug Hogarth's experiments with his atomic clock.
Smithsonian Institute - The Quartz Watch
History of the wristwatch, and a description of current technology.