by for example adjusting the processing parameters exemplary irregular conditions include the use of an incorrect punching tool 18 during the punching processing of the metal sheet 11 for example a punching stamp 15 and a punching die 16 with an excessively large diameter exemplary irregular conditions include further a partial stamp breakage of the punching tool 18 so that the punched out portion 28 has been cut only partially the processing result in the case of a partial stamp breakage can result for example in a faulty punched out portion 28 1 as illustrated in fig2 if a significant deviation of the actual extent of the punched out portion 28 from the desired extent is determined irrespective of the cause the drive motors of the coordinate guide unit 6 are stopped by the movement control unit 26 and the press drive of the press device 13 is stopped by the press control unit 27 furthermore the numerical control unit of the mechanical arrangement 1 generates an error message which informs the operator about the malfunction which has occurred alternatively or in addition a message suggesting modifications through the operator or a message showing the performed modifications can be generated as an alternative to the path 30 a path 32 of the detection movement of the laser beam 29 along the metal sheet 11 is indicated in fig2 for clarification the path 32 is illustrated to be displaced within to the circular edge 31 of the punched out portion actually the path 32 follows the desired contour of the edge 31 of the punched out portion 28 during the detection movement the laser beam 29 scans along the path 32 with its beam axis accordingly a portion of the cross section of the laser beam 29.