
Caesium Atomic Clock, 1955.
1955
1955
1956
1839 (original); circa 1988 (replica)
circa 1955
1955; 1830
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circa 1955
1957
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1956
2000-100 BCE
1955
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circa 1955
circa 1956
circa 1955
1955
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1990-96
1955
circa 1956
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1957