A time and date printing system is disclosed having a central electronic master clock (2) supplying clock pulses to subsystems (10) of groups of printers (14). Either the subsystems (10) or the printers (14) are coupled together in a daisy chain. The system enables a number of printers (14) to have accurate and guaranteed synchronised times as well as enabling the clock (2) to be sited remote from the printers (14) in a secure environment. A further embodiment is described and comprises a "standalone" arrangement but each of the "standalone" units share a common time source.
