master clock

noun

noun

A precision clock that provides timing signals to synchronise a slave clock as part of a clock network.

Special details of the new station are the crystal-regulated master clock in the concourse, which controls 11 "slave" clocks and will also control those to be installed in the Harlow Mill goods depot; [...].1960 September, M. J. Wilson, “Harlow Town station opened”, in Trains Illustrated, page 542:

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