How an atomic clock works, and its use in the global positioning system (GPS)

3-Second Blueprint (English)

1. A 5 MHz quartz oscillator drifts over time, so atomic clocks lock its frequency to hyperfine energy transitions in cesium vapor.
2. Magnets and microwaves route excited cesium ions to a detector; any current drop triggers a piezoelectric voltage pulse on quartz.
3. GPS intersects distance spheres from three satellites plus a fourth for clock correction, preventing 300 km per millisecond errors.