Apparatus adapted for use to reference a cam actuable switch or the like means to the disposition of a drive in a datum range (e.g.; the movement of a member between open and closed conditions under the action of the drive), said apparatus having, dependent on the drive, an eccentric member, a spur gear carried by yet free to rotate relative to the eccentric member, a ring gear with its inwardly directed teeth in an epicyclic meshing relationship with the spur gear, and a cam (or other datum providing interactive means component) [“cam”] rotatable with the spur gear adapted to interact, intended, capable of or suitable for being adapted to interact with a switch or the like means, wherein there is an adaption or a capability whereby both any such switch or the like means (save for its switch activation movement, if any) is or can be in a substantially fixed relationship with said ring gear when in use.