Hewlett Packard caesium beam frequency standard type 5061A
1972
1972
1990-1996
1980-1990
1980-1984
1987
1960-1970
1976
1979/80
1960-1970
1970-1980
circa 1982
1970-1980
1970-1978
1985-1990
1974
unknown
1972
1973
1965
1968
1981/2
1960
1960-1984