A printing system is disclosed which permits the printing of indicia on a continuously moving web at a fixed position offset from previously printed, evenly spaced web marks. The fixed position of the printed indicia relative to the web marks is independent of the velocity of the web. A web mark sensor, which may be part of the system to which the present invention is retrofitted, detects the passage of each previously printed web mark past a detection position. A registration circuit controls the timing of the printing of the indicia on the moving web and provides START signals for a servomotor-driven rotary print head which includes one or more peripherally mounted printing elements. A tachometer is mechanically coupled to a web transport mechanism to produce an output voltage which provides the velocity command for the servomotor drive of the rotary print head to match the rotational velocity of the print head to the linear velocity of the web during the printing interval. A STOP signal is produced by the registration circuit in response to the rotation of a vane, which rotates in conjunction with the print head, past a vane sensor to signal the rotation of a printing element to a rest position. A registration adjustment circuit permits the position at which the indicia are printed on the web to be varied.