Printing machine with a twin printing unit and method for operating such a printing machine

A printing machine for printing on a continuous web of printing material, the printing machine comprising:

• a plurality of in-line flexographic printing units disposed in a plane accessible to a machine operator;
• every two of said flexographic printing units of said plurality of flexographic printing units together forming a first double printing station or a second double printing station;
• said two flexographic printing units of a respective double printing station having a common impression cylinder;
• and
• said flexographic printing units in said first and second double printing stations being synchronized precisely in accordance with a register when changing print jobs to cause a switching from a first print job to a second print job and therefore a switching from one flexographic printing unit to another flexographic printing unit in said second double printing station to take place precisely at a point on the web of printing material where said first double printing station has completed a change.