Before revision: From the late 19th to the mid 20th centuries, electrical master/slave clock systems were widely used in public buildings and business offices, with all the clocks in the building synchronized through electric wires to a central master clock.
After revision: From the late 19th to the mid 20th centuries, electrical master/slave clock systems were widely installed in public buildings and business offices, with all the clocks in the building synchronized through electric wires to a central master clock.