A multiple nozzle continuous ink jet printer has a common nozzle block (10) with an array of nozzles (1, 2, 3, 4, 5, 6, 7) having respective charge electrodes (12) operated by respective drop charging circuits (45, 46, 47, 48, 49, 50, 51). A pilot nozzle (34) is provided in operative proximity to the nozzles (1 to 7) to monitor and detect changes in phase due to changes in ink parameters such as temperature, viscosity and pressure. A phase selection means (42) is arranged to alter the clock phase (33) applied to the pilot nozzle drop charging circuit (44) responsive to a sensor means (38, 40) thereby maintaining optimal charging by the pilot charge electrode (36). During system initialisation the correct break-off phase relationship is established for each charge electrode (12). During printing the phase selection logic (25, 26, 27, 28, 29, 30, 31) for the printing array (1 to 7) is altered based on the alteration of the clock phase to the pilot nozzle (34).