while the second group developed a system that was based on linear movement of switch components, which became known as the panel bank. As work continued, many subassemblies were shared, and the two switches only distinguished themselves in the switching mechanisms.

By 1910, the design of the Rotary system had progressed farther and internal trials employed it at Western Electric as a private branch exchange (PBX). However, by 1912, the company had decided that the panel system showed