Sometimes you can pick up a nice office clock or station clock at a bargain price. To ensure that these clocks all show the same time inside an organisation such as the railway system and avoid hassles with changing between winter time and summer time or replacing empty batteries, these clocks are normally connected to a clock pulse network that is driven by a master clock or radio signal. The master clock generates a pulse every minute, with successive pulses having opposite polarity.
If you want to use a clock of this sort, you naturally want it to keep good time. This is handled by the circuit described here.