An apparatus coupled with a mechanism and cooperating with the mechanism to locate an end-effector within a predetermined distance of a work site for situating the end-effector with respect to the work site includes: (a) a positioning unit coupled with the end-effector for moving the end-effector an adjustment distance with respect to the workpiece; (b) a sensing unit coupled with the apparatus for sensing extant locus of the end-effector with respect to at least one reference locus; and (c) an error determining device coupled with the sensing unit and the positioning unit; the error determining device determining a difference between the extant locus and the work locus. The positioning unit moves the end-effector in response to the difference indicating signal to reduce the difference.