Reference point calculation means calculates a reference point with respect to a reference axis direction, the reference point being a center position based on positions of a plurality of objects and the reference axis direction being a predetermined axis direction of a display area. A shuttle is movable through the passageway and has an intermediate portion exposed within the recess for manipulation by a user gripping the handle, and a suture-receiving-element at its distal movable axially through the distal end of the handle. The tower also comprises at least one coupling apparatus mechanically coupled to the mass assembly and to the tower, the coupling apparatus being operable to couple energy between the mass assembly and the tower as the mass assembly moves to and fro.