Abstract: The installation comprises several inspecting devices disposed along a track and controlling a switch. Each inspecting device is followed by a device for detecting the passage of the sheets, associated with a cyclic counter assigning a consecutive number to each sheet. A logic circuit directs the information from the inspection devices to reference memories the number of which is equal to the number of possible content conditions of the counters, (i.e. consecutive numbers) the information being directed to the reference memory whereof the number corresponds to the consecutive number of the sheet as assigned by the counters. Since the sheets are assigned numbers during their passage through the inspection region, it is possible to have several sheets simultaneously in this region.