consisted of a grid of vertical and horizontal brass bars with a hole at each intersection (c.f. top picture). The operator inserted a metal pin to connect one telegraph line to another. Electromechanical switching in telephony A telephony crossbar switch is an electromechanical device for switching telephone calls. The first design of what is now called a crossbar switch was the Bell company Western Electric's coordinate selector of 1915. To save money on control systems, this system was organized on the stepping switch or selector principle rather than the link principle. It was little used in America, but the Televerket Swedish governmental agency manufactured its own design (the Gotthilf Betulander design from 1919, inspired by the Western Electric system), and used it in Sweden from 1926 until the digitization in the 1980s in small and medium-sized A204 model switches. The system design used in AT&T Corporation's 1XB crossbar exchanges, which entered revenue service from 1938, developed by Bell Telephone Labs, was inspired by the Swedish design but was based on the rediscovered link principle. In 1945, a similar design by Swedish Televerket was installed in Sweden, making it possible to increase the capacity of the A204 model switch. Delayed by the Second World War, several millions of urban 1XB lines were installed from the 1950s in the United States. In 1950, the Ericsson Swedish company developed their own versions of the 1XB and A204 systems for the international market. In the early 1960s, the company's sales of crossbar switches exceeded those of their rotating 500-switching system, as measured in the number of lines. Crossbar switching quickly spread to the rest of the world, replacing most earlier designs like the Strowger (step-by-step) and Panel systems in larger installations in the U.S. Graduating from entirely electromechanical control on introduction, they were gradually elaborated to have full electronic control and a variety of calling features including short-code and speed-dialing. In the UK the Plessey Company produced a range of TXK crossbar exchanges, but their widespread rollout by the British Post Office began later than in other countries, and then was inhibited by the parallel development of TXE reed relay and electronic exchange systems, so they never achieved a large number of customer connections although they did find some success as tandem switch exchanges. Crossbar switches use switching matrices made from a two-dimensional array of contacts arranged in an x-y format. These switching matrices