machine, or calling device. Further development continued during the 1890s and the early 1900s in conjunction with improvements in switching technology.

Almon Brown Strowger was the first to file a patent for an automatic telephone exchange on December 21, 1891, which was awarded on November 29, 1892, as . The company later developed a rotary dial with lugs on a finger plate instead of holes that interrupted two independent circuits for control of relays in the exchange switch. The pulse train was generated without the control of spring