
Caesium Atomic Clock, 1955.
1955
1955
circa 1956-1959
1960
1959
1957
1960
1955
1958
(1962); 1982
1961
1958
1830 (original); 1967 (model)
circa 1956
1839 (original); circa 1988 (replica)
1956
1960
1961
circa 1955
1962
1960
1964
1955
1961-1962
1954-1955
1959
1955
1955
1957
1962
circa 1960
1957
1960
1963
1963
1960
1960
1955; 1830
1956
1956
1961
1963
1958
1955
1960
1954
1964
1964
1956
1954
circa 1955