color measuring instrument 6 and the register sensor 15 and can thus be used to determine the intensity threshold of the register sensor 15 the press 1 has a feeder 2 in which sheet printing materials 12 are separated and fed to a first printing unit 4 the printing units 4 5 each have impression cylinders 7 blanket cylinders 8 and plate cylinders 13 the latter carrying the printed image between the printing units 4 5 the sheets 12 are transported by transport cylinders 9 the transport cylinders 9 being assisted by a blown air guide 14 so that the transported sheets 12 have no contact with other parts the air metering of the blown air guide 14 is also carried out via the control computer 19 when the sheets 12 leave the press nip 10 between the blanket cylinder 8 and the impression cylinder 7 in the last printing unit 5 their color is measured by the in line color measuring instrument 6 in order to calculate in the control computer 19 the corresponding intensity threshold in each case for the subsequent register and position measurement for the control mark 17 18 to be measured this is done so quickly in the control computer 19 that the register sensor 15 arranged immediately after the color measuring instrument 6 is driven appropriately correctly with the suitable intensity threshold s so that it is able to register correctly the lines of the respective mark matched to the color of the respective control mark 17.