The invention relates to a method for controlling a printing machine (100) including a revolving transport device (10) for transporting a substrate (1000) printed or to be printed. The method includesa) continuously scanning the surface of the transport device (10) using a detection device (14); b) evaluating measured results to find defects (1001) on the surface; c) saving the defects in a datamemory (15), with repeated defects being evaluating additionally; d) outputting information on the defects. The method advantageously provides a machine operator (200) with targeted information on defect types, defect location and defect frequency, thus allowing targeted elimination of defects, which may increase the overall productivity of the printing machine (100).