Patent ID: 8532548

Claim:
Method for calibrating a printing machine comprising a plurality of printing units, the method comprising: transporting a first group of at-least-semi-transparent sheets at least once through the plurality of printing units; transporting a second group of at-least-semi-transparent sheets at least twice through the plurality of printing units, with the sheets being turned over between passages; printing a first registration mark on one of the sheets of the first group of sheets while the first group passes through the printing units; measuring the first registration mark at aregistration sensor located downstream of the plurality of printing units in the transport direction of the sheets; printing a second registration mark on one of the sheets of the second group of sheets during their second passage through the printing units, wherein no registration marks are printed on the sheets of the second group of sheets during their first passage through the printing units; measuring the second registration mark at the registration sensor; and determining calibration parameters usingthe measurements of the first and second registration marks provided by the registration sensor.