be changed has a directional characteristic 32 along the joining surface 16 of said frame parts for example which characteristic extends like a curtain within the intermediate space 17 preferably a very short distance a in the range of a few millimeters to at most a few centimeters for example particularly in front of the movable frame part 14 wherein a field width w of a first angular field of the directional characteristic 32 or of the sensing zone 37 of the sensor 31 said width being directed parallel to the adjustment path s of the movable frame part 14 is preferably much smaller than a field width u v orthogonal thereto of a second and or third angular field of said directional characteristic 32 or said sensing zone 37 wherein the field width u of the second angular field of the directional characteristic 32 is oriented in the axial direction of the at least one printing couple cylinder 04 mounted in the movable frame part 14 fig4 and the field width v of the third angular field of the directional characteristic 32 or the sensing zone 37 is oriented in the direction of a height h of the movable frame part 14 fig2 the directional characteristic 32 or the sensing zone 37 are therefore heavily concentrated at least in a direction in space which is opposite at least one of the two other orthogonal directions in space and therefore the directional characteristic 32 or the sensing zone 37 preferably extends flat along the joining surface 16 of the movable frame part 14 the field width u of the.