When synchronic time indication is required, the user often has a dilemma, what to choose. Clock networks, operating according to a master clock and client clocks principle, are available on the market. The master clock sets the time for all other devices. However, clock networks have some disadvantages: the master clock cannot be too far from the other electronic clocks; clock networks require connecting the clocks to form a network (attention! long, expensive cables). Such solutions are uneconomical, and the master clock failure "kills" the whole system. If you need to synchronise the clocks in several buildings, plants, or branches, which are several hundred kilometers away, the clock network must be connected through the Internet (it requires a permanent IP number). The voice of reason suggests: radio time synchronisation.

Time may be synchronised by radio in several ways. The first method is the RDS system of radio stations (amateur application - within a regional range). The other method is DCF77 signal, which is transmitted by ground  antennas from the town of Mainflingen, about 25 km from Frankfurt on the Main in Germany. The DCF system is not resistant to the interference of mobile phones or of high-voltage lines, the interference around industrial buildings or the interference of computer equipment. DCF77 is less and less significant, and the system itself is considered obsolete. The third method is the GPS system.