Clocks are flush mounted for the 10" or 12" size; and surface or double dial mounted for the 15" size. The 2 or 3-wire minute impulse secondary clock receives an electric impulse from the master clock once each minute advancing it one minute. Each hour, rapid impulses are emitted from the master clock to the secondary clock system by means of a third wire to provide hourly supervision of all secondary clocks. The 1-hour correction function will adjust clocks which are up to 20 minutes slow or up to 10 minutes fast. In the event of a power failure in excess of 58 minutes, all secondary’s will be automatically advanced to the correct time upon resumption of power.