Hewlett Packard HP 5061A Caesium Beam Frequency Standard, originally serving as one of a suite of ‘atomic clocks’ from the mid 1960’s onwards by the Greenwich Time Service, when it was based at the Royal Greenwich Observatory, Herstmonceux, Sussex. Hewlett Packard Caesium Beam Frequency Standard used at Royal Greenwich Observatory, Herstmonceux 1970-1978