I didn’t realize that there is a clock that runs on microwave signal. Atomic clocks use electronic transition frequency in the microwave region of the electromagnetic spectrum of atoms as the frequency standard for its timekeeping element. The principle of operation is not based on nuclear physics but on microwave signal that electrons in atoms emit. Atomic clocks are among the most accurate time and frequency standards. It is used in international time distribution services, to control the frequency of television broadcasts and in global navigation satellite systems.

The correct frequency for the particular cesium resonance is now defined by international agreement as 9,192,631,770 Hz so that when divided by this number the output is exactly 1 Hz, or 1 cycle per second. The long-term accuracy achievable by modern cesium atomic clocks is better than one second per one million years. Hydrogen atomic clocks show better short-term accuracy, approximately 10 times the accuracy of cesium atomic clocks. Therefore, the atomic clocks have increased the accuracy of time measurement about one million times in comparison with the measurements carried out by means of astronomical techniques.