fluid supplied via the line 17 a flowmeter 21 is provided which is connected to the process control system 30 with the aid of the line 26 another alternative for the embodiment in accordance with the invention can be a control system wherein the feed line 17 is connected with fresh water or clean sieve water and the feed line 16 of the low concentrate supply this embodiment is depicted in fig4 another possibility for regulating the material density across the machine width in the supply lines of the high concentrate and or low concentrate lines 15 16 leading to the headbox can include connecting these two supply lines to one another via another transport line 17 if now the concentration in the high concentrate line 15 needs to be reduced the amount of the suspension fed from the low concentrate line 16 to the high concentrate line 15 is increased or in the reverse case reduced this can for example occur with the aid of a speed controlled pump 20 connected to a flowmeter 21 such an embodiment is shown in fig5 fig3 and 5 describe measures by which the consistency in the lines 15 q h and 16 q l can be changed it can also be practical to change the proportion of q l q h without supplying additional sieve water line 17 by for example using the pumps 18 and 19 to regulate the proportions with all shown embodiments it is possible to obtain considerably better results in regulating the headbox of a paper or cardboard web manufacturing machine and to therefore improve the overall paper or cardboard quality that can be achieved with the present invention it is noted that the foregoing examples have been provided merely for.