zlacker

This was a centrally controlled clock. When the master clock sent a pulse, all the clocks would advance 1 minute.

These were synchronized wired clocks ( https://www.natsco.net/industries-served/industries-served-o... /// https://blog.american-time.com/wireless-master-time-clock-vs... ).

> Schools traditionally used wired clock systems for two basic reasons: rock solid reliability and the ability to synchronize school bells to the rest of the system. The wired synchronized system ensured that clocks would all read the same time and bells would ring at the same time every day, no matter what classroom you were in, and that students would arrive to class on time — something teachers could only dream of before installing a synchronized system.