Possible folds produced in the paper web that remain unnoticed can have far-reaching consequences during processing and often lead to unusable printed products. Extreme differences in printing registration, i.e. inaccuracies when correlating overlapping colours may also occur. Another risk is that the paper web tears while going through the print machine. Any machine stoppages or changeovers can significantly increase printing costs. Non-contact, optical measurement technology is a suitable solution.