- 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.
