pierce through the radial surfaces and are arranged between at least one not shown light source and at least one not shown light actuated apparatus the markings 7 fulfill operation for the gray code so that by the step wise transition from one rotary position to next following rotary position single one of the markings is changed while the other three markings remain unchanged the value embodying carrier 11 is driven by a not shown driving means for example from a shaft the rotary position of which is to be controlled positioning of the shift element 4 in engagement with the altered pinion 5 rotates the pinion shaft so that the pinion 17 located on the same shaft which is in engagement with the ring gear 8 of the second value embodying carrier 12 is stepped by one position by this transition are corresponding signals produced without thereby passing through undesired intermediate stages as is the case with known counters on the front side of the value embodying carrier 12 it is noted that the marking 7 the radial slits are symmetrically formed to a connecting line of the shift elements 4 in other words the value embodying carrier 12 passes through with one revolution for example with.