And then there were the "unusual" relay configurations, such as latching relays (apply one pulse to the coil to turn it on, another pulse to turn off), dual coil relays (one coil for on, one for off), and stepping relays (multipole switches, with each coil pulse advancing the output position by one "step". They usually had a separate "reset" coil, which would jump the output back to "zero" when pulsed. These were widely used for telephone exchanges, counting pulses from rotary dials to complete calls. Originally called a "Strowger switch" after the inventor.
