[photopress:NISTF01_clock.jpg,full,alignright]The China National Institute of Metrology Science has declared that the latest NIM4 laser cooled Cesium fountain clock is running reliably and stably.
So what is reliably and stably? The accuracy allows an error of 55*10-15. More understandably it may lose or gain a second or less every six million years.
China is one of the few countries in the world that has its own independent, time-frequency system.
The unit(s) of the second is one of the seven most important basic physical quantities defined by the international system of units (SI).
In 1967 the General Conference on Weights and Measures (Conference Generale des Poids et Mesures, CGPM) decided to change the definition of a second from the astronomy second to the cesium atomic second. Since then, the laboratory-cesium atomic clock has provided the basis for the definition of the second and become the benchmark device for measuring time and frequency.
As a basic physical quantity, time frequency plays an important role in the national economy, defense and basic scientific research. In the last 10 years, three Nobel Prizes for Physics have been awarded for achievements related to time and frequency standards.
(Our illustration is of the original NISTF01. The Chinese clock is several generations on. It is, however, still more than wristwatch size although smaller than that illustrated.)
Source: People’s Daily Online
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