Power unit for the exchange meter, by Alos Ag, Switzerland, 1960-1970

The process of billing customers for their telephone calls was made significantly easier by photographing the meters in batches using a specially-adapted camera. The readings could be transcribed more comfortably in another part of the exchange and a permanent record resulted which was useful evidence in case of dispute. Although the Science Museum already had examples of different kinds of exchange meters no other billing equipment was held, so this camera illustrated a part of the telephone business sometimes overlooked.