A simulation system for simulating a function of a biological organ using a biological model in which the function of the biological organ are represented by a mathematical model with a computer is provided. A clipping process is performed for a first object lying across the near plane while a second object lying across the far plane is exempted from the clipping process. In a case where an instruction to perform a reading job in the one mode is received while the other mode gain setting processing is being performed, the image reading device discontinues the other mode gain setting processing and performs the reading job in the one mode. In one embodiment, an \u201cF\u201d style clamp may be made with one or both of the two cooperating jaw members or sections being cast from a magnesium compound or alloy. The dither control signal can alternate between a plurality of states or pseudo-randomly switch between a plurality of states.