A sterile drape for a trackable medical device includes a reinforced film portion and a holding or tensing device. For example, in one embodiment the stock includes an upper portion. The add on filter includes an ultraviolet light source for emitting a broad spectrum of ultraviolet light and a catalytic target structure mechanically coupled to the ultraviolet light source. The TV tuner is easily combined into and removed from the display apparatus. One, or more, inserts are inserted between the box spring and mattress andor placed on top of mattress until desired comfort is achieved. The model framework provides built-in functionality that defines a default behavior.