An apparatus for assembling over a standard electrical wall outlet for providing a handy and neatly stored retractable extension cord disposed in such apparatus. The system includes a level detector configured to receive an input signal and produce, at least indirectly, a reset signal when the input signal reaches a predetermined level. The dining board is connected with two links which are pivotably connected to the legs of the backrest so that the dining board is pivoted and positioned horizontally. Th PCUs are also used to compute arbitrary depth values which, unlike traditional interpolated depth values and modified depth values, are not dependent on the coordinates of the geometry primitive with which the arbitrary depth values are associated.