journaled on the support base plate 62 and a bendable wire rope 124 having a flexibility is reeved around the rope guide 122 one end of the rope 124 is connected to the disc member 118 the other end of the rope 124 has a metal terminal 126 and the terminal 126 is connected to a projection of the element 110 when the terminal 126 is positioned at a control end of the rope an initial zero position of the spring 120 is set so that the tension on the rope 124 from the spring 120 becomes zero and also a spring 120 is employed which has a spring constant corresponding to the weight of the base plate 84 scale mounting plate 86 and scale the cylinder 116 disc member 118 coil spring 120 and rope 124 are connected to an eccentric position of the gear 104 namely the rotating member 104 and elastic means is connected to the rotating means 104 which provides a rotary force in a direction opposite to the direction due to the weight of the scale of the rotating member 104 also the guide groove 108 element 110 shaft 112 and knob 114 constitute a mechanism for shifting the.