Abstract: A method of observing a moving web having printed thereon a regularly repeated pattern comprising moving said web past at least two photoelectric cells mounted so as to observe simultaneously or substantially simultaneously a predetermined group of control features on the web, and initiating a cutting and/or controlling operation whenever such observation occurs.

Abstract: A method for observing a moving web having printed thereon a regularly repeated pattern and control features along the web, comprising mounting two photoelectric cells a fixed distance apart in the direction of movement of the web, the photoelectric cells being adapted simultaneously to scan identical data in different locations on said web, the cells being connected in an electrical circuit which is balanced when they observe identical data and which produces an output when they observe non-identical data due to one cell but not the other observing a control feature.