the second inner hydraulic cylinder 113 c thus the two pairs of series connected hydraulic cylinders 113 a 113 d 113 b 113 c can be connected in parallel so that one and the same supply line supplies a first side of a hydraulic cylinder of each couple and one and the same return line receives hydraulic fluid from both pairs furthermore one of the outer hydraulic cylinders 113 a and one of the inner hydraulic cylinders 113 b can be provided with associated position sensors 118 119 the position sensors 118 119 are connected to a control unit 120 analogously with the control unit described above which may also comprise a presentation device 121 and an input device 122 and which may be adapted to control the hydraulic system fig7 a shows the seeder 100 from behind when located on flat ground in this position all the wheels 112 a 112 d are located at the same distance from the transverse beam 110 b fig7 b shows the seeder 100 in a state where the two middle wheels run in a pair of grooves 4 made by the towing vehicle in this case owing to the design of the hydraulic system the amount of hydraulic fluid will be distributed between the cylinders 113 a 113 d in such a manner that each wheel is in contact with the soil surface 3 and the load is evenly distributed over the wheels this reduces the risk of an unevenly distributed load affecting any one of the wheels it also reduces the.