An incremental measuring instrument having a series of reference marks extending alongside a division of a scale is provided with a selector element which is slideable along the length of the scale and can be aligned with a selected one of the reference marks in order to bring the selected reference mark into operation. The position of the selector element with respect to the selected reference mark is fixed by a plurality of filler elements which cooperate with a selector element to form a column of elements arranged end to end within a guide. Holding elements at the ends of the guides preclude undesired longitudinal movement of the column of elements.