This was one of the last, if not the last, [PBX telephone exchange](http://en.wikipedia.org/wiki/Private_branch_exchange) to utilize electromagnetic relays. All subsequent exchanges used transistors and electronic circuitry. My resposibility was the total packaging of the exchange, including the exterior cabinets, the control panel, as well as some interior changes to accommodate the smaller, lighter and more manageable cabinets. Production began in the mid-sixties. -Lawrie McIntosh