Holtzer Cabot Clock from Cali Show

[Owain]

Since they had no timekeeping mechanism, the slave clocks were very cheap to make, and many of them could be installed.

Those qualities about the slave clocks are true, but I think the overriding reason these were installed is because they were installed in places where a standardized institutional time was imperative, for example, in a large school where all the classes have to start and stop at exactly the same time, and in factories where work shifts must all start and stop at the same time.

There was also the significant labour cost of winding clockwork clocks and resetting them to summer/winter time. Mains synchronous clocks, even once available, were expensive, needed a reliable AC mains supply (some parts of the UK still had DC mains into the 1950s I think) and still needed resetting for summer/winter time.

In factories the pulses could also be wired into process timers.

I once worked briefly in a 1920/1930s factory building that still had a master clock, not sure if the slave displays were connected, and also a 'drop flap' electric fire alarm control panel.