A tachograph for a motor vehicle comprises a guide element for guiding a paper strip in relation to a printing group. When the projections are connected to each other the user will not breath onto the lower front hood portions. Thus, it is possible to prevent a bus from being distributed to a predetermined master, and it is possible to improve overall performance of a bus system by solving a problem of unbalanced distribution of performance between the plurality of masters. By merely pushing the mounting convex portion in the mounting concave portion, the sealing plate and the piston can be integrated, which improves productivity in assembly.