In the United States there were a number of private time services one could subscribe to. One of the largest was operated by Western Union. A telegraph line w

In the United States there were a number of private time services one could subscribe to. One of the largest was operated by Western Union. A telegraph line would be used to send a synchronized signal a short period before the top of the hour, which energized a solenoid in the clock. The minute hand would be pulled to the :00 position and the clock would restart once the signal was released. Commercial telegraph message traffic would be offline until this signal was completed. https://www.hemmings.com/blog/article/tick-tock-whirrrrrr-thunk/ https://www.hemmings.com/blog/article/tick-tock-whirrrrrr-th... There were also thousands of local "master clock" installations in schools and other facilities. Lots of kids from the 70s and 80s probably remember the IBM school clock: https://www.schoolhouse.com/products/1960s-ibm-standard-issue-clock https://www.schoolhouse.com/products/1960s-ibm-standard-issu...