Rotary dial Tesla

The rotary dial was a key component of the automatic phones since the beginning of their production. By dialing a number, a spring is wound and after the dial is released, it returns to its base position and a certain number of impulses is generated, depending on the number dialed. The speed is stabilised with a Watt friction regulator. The telephone exchange would count the number of impulses and create the desired connection. Metal components of the dials were replaced with plastic ones during the production years, but this affected their reliability.