Abstract: A sheet-representing signal is registered by successive shift-register stages in simulation of the travel of a sheet through a printing machine. Signal detectors connected to different register stages actuate moving units which in turn change the state of activation of the functional units of the printing machine. Upon a changeover from one-side to two-side printing, there arises a sheet travel path length change composed of a fixed component determined by machine geometry and a variable component determined by sheet length. Each moving unit moves cyclically and can move the associated functional unit only during a certain portion of the cycle. Upon a printing mode changeover, moving units undergo a phase shift of their cycles of motion and signal detectors are disconnected from certain register stages and reconnected to others, thereby compensating for the variable and fixed components of the sheet travel path length change.