This definition is based on the operation of a caesium atomic clock. A number of other atomic clock schemes used for other purposes. The requirement that an aircraft be equipped with an atomic clock precludes its general use. Other signals send out the time as measured by the satellite's onboard atomic clock. Computers often set their time from an Internet atomic clock source. The atomic clock works on differences in magnetic spin. The Atomic Clock Ensemble in Space is an example of clock research. NMC maintains five caesium atomic clocks and one hydrogen maser atomic clock. For example, all of the best atomic clock technologies involve Doppler cooling at some point. In addition a rubidium atomic clock is available on site. The INSAT-1 is set to carry a miniature atomic clock and a GPS receiver. Other satellites and payloads included Oculus-ASR nanosatellite, GPIM, and the Deep Space Atomic Clock. Additionally, the technique can be used to construct an atomic clock with great precision. For highly accurate measurement of time an atomic clock is used. In August 2004, NIST scientists demonstrated a chip-scale atomic clock.