National Frequency Standard: NIST-7
NIST-7: the seventh generation of atomic clocks at the National Institute of Standards and Technology.
Unveiled on April 22, 1993, it kept time with an initial uncertainty of less than three parts in 10 to
the 14th (3E14), equivalent to one second in a million years. The expected uncertainty after evaluation
is less than one second in three million years (1E14).
The standard is shown with three of the researchers who spent seven years developing it. From left to
right are John P. Lowe, Robert E. Drullinger (Project Leader) and David J. Glaze.
Photo courtesy of National Institute of Standards and Technology Boulder Laboratories, U.S. Department
of Commerce.
Clocks
UBR, Inc. Revised 8 Dec 1994
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