Credit: GMaple Design/shutterstock.com Greenwich Mean Time In the previous essay I introduced mean solar time, which averaged the annual variation in apparent solar time so as to generate a time scale that was more consistent with the time scale generated by clocks that used a mechanical device to realize the reference frequency. The device that generated the reference frequency might produce an event every second, but other configurations were possible. In every case, the device that generated the reference frequency was coupled to a second system that converted the reference frequency to a series of one-second ticks that were used to drive the clock display. The source of the reference frequency and the counting system were designed together to generate the one-second ticks.