Abstract: A plurality of electrically conductive plates, preferably ring-shaped, are spaced from one another and electrically insulated from a conventional conductive probe rod, but movable therewith. The sizes and spacing of the plates are selected to provide a desired variation in capacitance between the plates and the object as the probe rod and the plates are moved toward the object. The capacitance between the probe rod and the object also increases as the probe rod moves toward the object. By appropriately combining these two capactiances, a nearly consant net capacitance occurs when the probe tip is very near a desired distance from the object, for a range of object sizes.