been assumed that the distance determined by the counter s2 amounts to 100 mm the counter s2 25 stores a pulse number corresponding to the number of pulses that are generated as the web travels between consecutive printed marks in the fig3 a example it is assumed that the printed marks are spaced 500 mm apart in response to the movement of each printed mark 12 past the photodetector 17 the latter generates a mark pulse di and a remainder determining circuit 24 see fig2 operates in accordance with the formula k1 n u00d7 s1 where k1 is the distance between the sensor for the first pulse generator 15 and the photodetector 17 for the mark pulse generator n is an integer and s1 is the spacing between successive printing marks 12 to subtract the value s1 from the machine constant k1 until an integral remainder that is smaller than s1 has been obtained in accordance with the fig3 a example 800 1 u00d7 500 300 mm referring again to fig2 at the junction 27 the value s2 is subtracted from that remainder in accordance with the fig3 a example 300 mm 100 mm 200 mm the set point for the automatic control has thus been determined the actual value is determined by the counter i1 26 which counts the pulses generated from the time.