+An **atomic clock** is the most precise timekeeping device, measuring time by the unchanging [resonant frequency](/wiki/resonant_frequency) of atoms. Often using [cesium](/wiki/cesium), these clocks define international time scales and are vital for global navigation and satellite systems.
+## See also
+- [Time](/wiki/time)
+- [Frequency](/wiki/frequency)
+- [Metrology](/wiki/metrology)