of the slice a of the headbox 30 after the slice part and the forming gap g the twin wire zone passes through the wire part 50 and further to the press section 41 in the wire part 50 and in the press section 41 the web w is dewatered mechanically after which the web w is transferred to the dryer section 42 where it is evaporation dried the profile bar 33 and the slice a are profiled by means of a regulation system which comprises a series of regulation rods 32 attached to the profile bar 33 rods 32 are regulated by means of a series of actuators 31 the profile regulation means 31 32 receive their regulation signals s p from a process control system 100 a measurement arrangement for the transverse grammage profile of the web w which is placed in connection with the dryer section 42 gives a series of measurement signals m p to the process control system 100 on the basis of measurement signals m p the process control system 100 controls the profile of the profile bar 33 of the headbox 30 and at the same time the transverse profile of the pulp suspension jet j so that in the finished dried web w a grammage profile is carried into effect that is as uniform as possible in the cross direction during drying it is a known phenomenon that the web w shrinks in its middle area less than in the lateral areas the shrinkage being in the middle about 4 and in the lateral areas from about.