The invention relates to an operating element for adjusting the cross-hairs of a telescopic sight. The operating element is in the form of a rotating knob, arranged to rotate on the telescopic sight, whereby a rotation of the rotating knob adjusts the cross-hairs by means of an adjuster mechanism. The rotating knob comprises one or several index marks, by means of which one or more positions of the cross-hairs may be indexed. The one or several index element(s) is/are arranged in one or several recess(es) and may be displaced therein in the circumferential direction of the rotating knob. The index elements are furthermore coupled to the rotating knob in the recesses such as to be rotated with the rotating knob on a rotation of the same. According to the invention, the outer surface(s) of the index element(s) are recessed relative to the outer surface of the rotating knob in the direction of the rotational axis of the rotating knob and the one or several index element(s) is/are arranged to be permanently displaceable in the recess(es).