
Caesium Atomic Clock, 1955.
1955
1955
1955
1955
1830 (original); 1967 (model)
1839 (original); circa 1988 (replica)
1955
1955
1955
circa 1955
1955
1955; 1830
1955
1955
1954-1955
1954
1955
1954
circa 1955
1955
1954
1955
1954
1954
1954
2000-100 BCE
circa 1955
1955
1903 (original); 1982 (model)
1954
1955
1990-96
1955
1955
1954
1954
1955
1954
1954
1954
1954
1955
1954
1955
4000-2001 BCE
1955
1954
circa 1955
1990-95
1955
1955