Doing a bit of Internet archaeology I have found that the image that Michael posted was from here
https://www.ebay.com/itm/VINTAGE-IBM...-/283531227466
but I still can't get enough resolution to read the label.
This seems to be the same model
https://www.ebay.com/itm/VINTAGE-IBM...-/283531227466
If so, I confess I don't know how it works, because it seems to have a 115v 60Hz motor
and a clutch magnet actuator.
<wild_guess>
So does that mean it runs like a conventional electric clock, and gets reset to 12:00 by the master every midnight?
</wild_guess>