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