which is connected to the part 1 by means of a piston 15 of a piston rod 8 the piston 15 is guided in the second annular cylinder 12 by means of a second guide face 20 as can easily be recognized in fig1 each monitoring body 7 has the shape of a ball seven balls 7 can be seen in the chamber 4 fig3 the diameter of these seven balls 7 is more or less equal among the seven balls 7 there are two types of ball 7 which differ from one another in terms of a physical parameter in the present exemplary embodiment the parameter characterizing the balls 7 is electrical conductivity i e four balls are electrically conductive and the remaining three balls are manufactured from an electrical insulator in fig1 these balls 7 are illustrated in a monitoring arrangement in which when seen in a spatial manner said balls 7 are arranged in one level along a peripheral circle this level lies more or less parallel to the end face 18 of the second annular cylinder 12 the peripheral distance between the balls 7 is determined by segment shaped dents 10 in the contact area 17 of the first annular cylinder 5 the shape.