#44 Caesium atomic clocks have been used as a reference standard since the 1950s. This one is unusually big though, look for "HP 5060A" for a more normal sized one (released in the 1960s).
#44 Caesium atomic clocks have been used as a reference standard since the 1950s. This one is unusually big though, look for "HP 5060A" for a more normal sized one (released in the 1960s).