Keywords: Atomic Clock015.jpg NIST-7 The seventh generation of atomic clocks at the National Institute of Standards and Technology It was unveiled on April 22 1993 and keeps time to an accuracy of one second in one million years When this clock was fully evaluated approximately a year after its unveiling it had an accuracy of one second in three million years and was the world's most accurate clock National Institute of Standards and Technology 1993-04-22 National Institute of Standards and Technology PD-USGov-NIST PD-USGov National Bureau of Standards National Institute of Standards and Technology Atomic clocks |