The master clock is the controller for a synchronized time system. The master clocks originally were very accurate wall regulators that were pendulum regulated and self winding. These clock systems were used by schools, factories, government facilities, railroads and actually any entity that desired a number of clocks to provide the exact same time. One master clock would control almost any number of secondary or slave clocks. All the secondary clocks were connected by wires to the master clock. These systems were direct current and originally powered by batteries.

Master clock-slave clock systems began to appear in  the 1880’s and synchronized time systems were found in most large buildings by the 1920’s. In the United States the earliest manufacturers were The Time Telegraph Company, The Self Winding Clock Company and The Standard Electric Time Company. By the 1890’s, and as late as the 1930’s, several other companies began to offer their own versions of synchronized time systems. Alternating current clock systems appeared in the 1950’s and became the system of choice however many of the original DC systems remain operational to this day.

We have begun to assemble pictures and information for many of these companies. We welcome other collectors to contribute photos and company information.