Abstract: A plow beam 4 is coupled to a tractor chassis 1 by a three-point linkage having a top link 9 and two bottom links 3. The top link 9 is a double acting control ram 23 which has hydraulic couplings 26,28,25 and 27 which cross-couple the control ram 23 to a double acting sensor ram 21 so that expansion of one ram produces contraction of the other. The sensor ram 21 is coupled between a pivot 17 at the head of the lift rod 18 of a conventional lift mechanism for the plow, and a pivot 22 on the tractor chassis. Movement of the lift rod 18 due to height variation of the plow beam 4 actuates the sensor ram 21 to vary the length of the top link 9, so as to vary the pitch attitude of the plow. Good land profile following is achieved by a high rate of change of pitch at normal working depth. A lower rate of change is achieved as the plow is raised out of work.