The economic development of a step-by-step automatic telephone equipment

Since Campbell published his paper in 1910, modifications have been made on the step-by-step telephone equipment. This paper covers a review of the economic development of this system with particular emphasis on the technical development in general. The material is grouped under development of circuits and trunking, mechanical design, manufacturing methods, maintenance improvements and possible future developments. Saving in equipment and trunks is considered under the switching selector repeater, director and frequency selecting connector while the reduction in maintenance cost is shown by the reduced number of troubles per line per month when comparing the newer developments with equipment installed fifteen years ago.