Abstract: A coupling device is provided for coupling the movable member of a machine to a potentiometer to convert sliding movement of the member into proportionate movement of potentiometer. The device includes a first rod which is attachable to the movable machine member and a second rod which is connectable to the potentiometer. A ball-shaped slide is attached to the first rod and a planar abutment is attached to the second rod. The glide piece and the abutment are in abuting contuct with one another. A biasing spring is provided which applies pressure, in a working direction, to the glide piece to thereby maintain the glide piece and the planar abutment in intimate engagement with one another. This arrangement forms a joint connection between the first and second rods which enables transmission there between of only translational movement.