68.The first atomic clock was built in 1955.

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atomicclock
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timekeeping
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precision
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frequency
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cesium
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technology
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innovation
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science
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accuracy
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standard
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quantum
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physics
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oscillation
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electron
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transition
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radioactive
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nist
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utc
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gps
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navigation
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aerospace
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telecommunication
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calibration
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metrology
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atomictimescale
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timesignal
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clockface
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display
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synchron
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network