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The first caesium clock was built by Louis Essen in 1955 at the National Physical Laboratory in the UK [1] and promoted worldwide by Gernot M. R. Winkler of the United States Naval Observatory. Caesium atomic clocks are one of the most accurate time and frequency standards, and serve as the primary standard for the definition of the second in ...
Atomic clocks have the benefit that atoms are universal, which means that the oscillation frequency is also universal. This is different from quartz and mechanical time measurement devices that do not have a universal frequency. A clock's quality can be specified by two parameters: accuracy and stability.
NIST-F1 is a cesium fountain clock, a type of atomic clock, in the National Institute of Standards and Technology (NIST) in Boulder, Colorado, and serves as the United States' primary time and frequency standard. The clock took fewer than four years to test and build, and was developed by Steve Jefferts and Dawn Meekhof of the Time and ...
The majority of the clocks involved are caesium clocks; the International System of Units (SI) definition of the second is based on caesium. [6] The clocks are compared using GPS signals and two-way satellite time and frequency transfer. [7] Due to the signal averaging TAI is an order of magnitude more stable than its best constituent clock.
NPL-CsF2, Yb+ and Sr+ ion clocks, Sr lattice clock, 4 hydrogen masers [5] [6] National Physical Laboratory; ... 18 cesium atomic clocks and 4 hydrogen maser clocks
Mechanical clocks kept the mean time, as opposed to the apparent time displayed by sundials. By that time, sexagesimal divisions of time were well established in Europe. [nb 4] The earliest clocks to display seconds appeared during the last half of the 16th century. The second became accurately measurable with the development of mechanical clocks.
The exact modern SI definition is "[The second] is defined by taking the fixed numerical value of the cesium frequency, Δν Cs, the unperturbed ground-state hyperfine transition frequency of the cesium 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s −1." [1]
In the International System of Units (SI), the unit of time is the second (symbol: s). It has been defined since 1967 as "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom", and is an SI base unit. [12]