![]() Offset against this were a couple of nuisance factors: Early synchronous clocks were not generally self-starting, so even a minor glitch in the power would require a visit to every clock in the building to set it going again. ![]() The electrical supply company took over responsibility for this function by maintaining their average network frequency within very close limits. Synchronous clocks offered the advantage of inherently reliable timekeeping. In contrast, impulse clock systems used one accurate master clock to control any number of remote slave dials over a dedicated low-voltage circuit. Synchronous clocks, powered by the AC mains electrical supply, use the precisely-controlled mains frequency to keep time. Before the advent of quartz electronic clocks, which enabled low-cost clocks to offer excellent timekeeping performance and run for years on a battery, there were two types of electric clock offering high accuracy that were suitable for use in quantity throughout large premises.
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