In New Zealand we used a similar technique to upgrade electromechanical telephone exchanges to STD (Subscriber Toll Dialing) in the 1980s. To 'program' the calling subscriber's number into the system we would feed a wire through several levels of ferrite rings, one level for each digit. A tone was sent through the wire and the rings acted as current transformers, producing voltages that were detected and operated relays which encoded the phone number (used to bill the subscriber for the toll call).
I helped install this equipment into the Hastings (NZ) telephone exchange. The rings were mounted on iron racks that went from floor to ceiling and (literally) weighed a ton. We had to unpack them before hoisting up to the 1st floor of the exchange. Two of us were holding onto opposite ends of a crate while another jemmied it open. He got a bit too keen and pushed it over. I could feel the weight was too much so I jumped back and the rack crashed to the ground on its back, bending all the pins flat against the rings. We installed it just like that because bending the pins straight again would probably break them off. Luckily no ferrite cores were broken in the fall!