A method and an arrangement is disclosed for the detection by photoelectric means of markings made on a printed, decorated material web. The markings comprise two groups of stroke markings, the markings of a first group being arranged to be sensed by a first photocell element, which, on sensing the first group markings causes the output of a second photocell element, which senses the stroke markings of a second group of making to be fed into a memory unit for continuous comparison with a stored value. In response to the comparison, a control signal is generated to control the performance of various operations on the web.
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