Good afternoon!
I am beginning to sound – to myself at least – like a broken record, but the foremost expert I know on these is Ken Reindel of kensclockclinic.com
If he doesn't know about it, it's probably not worth knowing.
When I worked in broadcasting, we had these in all the studios. Ours were the sweep-second type, with lots of largely ineffective soundproofing inside. (Announcers often said, "You can always make the clock wind itself by opening the mike.") By the late 1960s, Western Union was working with the phone company. They sent a 90v AC ringer pulse down a phone line at the top of the hour to a relay housed in our phone wiring cabinet. This relay provided a contact closure to all of our clocks. The contact closure caused the synchronizing solenoids to pull and the red light above the numeral "6" to light up momentarily.
All our clocks worked on two, 1.5v #6 cells, which were, as I recall, good for about 6 months or so. Western Union sent a guy out to replace the cells and check the operation of the clocks at regular intervals. We didn't have to do anything. In those days, if memory serves, we paid $6 per month per clock to have highly accurate time in the station. This was essential for scheduling, and especially for interacting with the network.
Some stations, I heard, used the synchronizing relay to actuate a 1000-cycle tone at the top of the hour. This was fed into the mixing board, so that you always got a time tone over the top of whatever program was running at the beginning of the hour.
Clocks like the one you have, without the sweep-second hand, were often found in public buildings. At one time, as I recall, the entire NYC subway system was full of SWCC clocks. The famous 4-sided clock in the middle of the information booth in Grand Central was a SWCC product, though my understanding is that it has been reworked, since the SWCC service is no longer available.
Good luck, visit Ken's site, and best regards!
Tim Orr