A multiple-level undoredo mechanism is provided in an operating system and is available to application programs run on the operating system. A pixel structure according to exemplary embodiments of the invention include a plurality of pixels disposed in a delta arrangement, each of the plurality of pixels having four sub-pixels that are four divisions divided from the pixel, and divided sides of the sub-pixels are arranged in a vertical direction or in a horizontal direction. In this way, the heat exchanger functions to augment the cooling capabilities of the evaporator. Water flowing through the pipe is sequentially heated by the first and second heating elements. It also determines the changes needed to pre-process inputs in order to achieve production at design targets.