The Master / Slave Clock setups are basically the situation where there is a single master clock that controls the slave clocks or slave dials (as they are often called). The master clock traditionally tells the slaves as each segment of time passes, thus the master clock keeps updating the slaves. This clock setup is extremely useful in the situation where maintaining many clocks to the same clock time is required. Such as clocks within a factory, school, train station, office building, airport, etc.... Maintaining the correct time from one central clock or point is much more cost effective than having to individually visit all the clocks to adjust them.

How does the master clock maintain the slaves? Basically it is done by wiring the clocks togethor in a circuit and sending out an electronic pulse from the master. The slaves update each time they receive a pulse (i.e. every second or every minute). This system can also have other elements associated with the system, such as bells and fire alarms which can be programmed to sound at specific times. This master/slave clock setup was also attached to punch clocks for factories that use clock on/off time keeping.

The master/slave clock setups began appearing in the early 1900's and in many cases they have not changed that much from the original setups as described above. But in saying that a new master/slave clock setup has started to evolve. The new setups are different in that the slave clocks are real clocks that resynchronize with the master, and are not just dials. The new setups are commonly called atomic wall clocks or radio controlled clocks or even r-wave clocks. These clocks are not wired togethor but are resynchronized by either a signal from the mains power or a radio signal. The master clock is an atomic clock, and the slave clocks are available to the general public.