"up" with the keys in the normal position so the parties can converse. The supervision lamps light to alert the operator when the parties finish their conversation and go on-hook. Either party could "flash" the operator's supervision lamps by depressing their switch hook for a second and releasing it, in case they needed assistance with a problem. When the operator pulls down a cord, a pulley weight behind the switchboard pulls it down to prevent it from tangling. On a trunk, on-hook and off-hook signals must pass in both directions. In a one-way trunk, the originating or A board sends a short for off-hook, and an open for on-hook, while the terminating or B board sends normal polarity or reverse polarity. This "reverse battery" signaling was carried over to later automatic exchanges. Some areas used specialized switchboards to handle calls from payphones. In North America, these "coin boards" were gradually phased out after the introduction of the Automated Coin Toll System that was provided by the Traffic Service Position System. Dedicated coin boards were primarily used in large, densely populated areas such as New York City where the large local calling area required special billing arrangements to allow the rate for a local call to vary based on the distance called. In less densely populated regions, calls from payphones were handled by normal assistance operators without the use of dedicated coin boards. References Further reading Atlanta Telephone History: Part 1 - Early Telephone Service especially the section from 1905 on. History of telecommunications Switchboard