Device for presetting a cut-off register in a folder of a web-fed printing press

Device for presetting a cut-off register in a folder of a web-fed printing press, comprising a marking device for applying at least one mark in an image-free region between two printed images of a web, detector means for detecting the image-free region on the web, said detector means being connected to said marking device for signalling said marking device when the image-free region is detected thereby, said marking device being disposed a defined distance in front of a nip located between cylinders of at least one printing unit, and means for activating the marking device to apply a mark to the image-free region of the web when a respective output signal of said detector indicates the presence of the image-free region on the web, at least one of the cylinders being a blanket cylinder having a gap formed therein, and said detector means having a reflecting detector for scanning the surface of the blanket cylinder, said defined distance at which said marking device is disposed in front of said nip corresponding to a circumferential distance extending from a measuring location of said reflection detector to said nip, said marking device being actuated when the gap formed in the blanket cylinder is detected by said reflection detector.