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Caesium Atomic Clock, 1955.
1955
1955
1932-05-06
1940-1960
1915
1918
1926, May
circa 1950
1943-1944
1943-1944
1943-1944
1949
1932-05-06
1932-05-06
1905-1911
1958-1967
1950-1958
1954
1943-1944
circa 1934
20th Century
1899
1964-1965
1911
1970-1972
1965-1968
1940-1960
1901-1927
1924
1916
1912-1930
circa 1948