rapid advancing movement and the dynamic stability of the system is favored instead such control resolution can be obtained according to the description and the showing in fig4 with the employment of seating valves as synchronizing valves by leaving a free space 40 according to fig3 between the mechanical control element of the valve and the mechanism of the error measurement system there results from this a dead play of the valve as fig4 more fully illustrates when the beam 16 set in motion through the rapid advancing motion passes a point that has been preselected by the operator such preselection can be accomplished for example by means of an adjustable mechanically actuated electric switch then the two port two way valve 4 4 39 which directs the oil flow from the pump 1 to the upper annular chamber 2b 2b 39 of each of the cylinders 2 2 39 is brought to its normal rest position which is its open condition thereafter like pressures exist in the inner chamber 2a 2a 39 and in the upper annular chamber 2b 2b 39 of each of the cylinders 2 2 39 and the said chambers are fed with an oil flow which is a combination of the flow from the pump 1 and the oil flow escaping from.