A certain amount of spoilage, rework, or scrap is inherent in many production processes. For example, semiconductor manufacturing is so complex and delicate that some spoiled units are inevitable due to dust adhering to wafers in the wafer production process and crystal defects in the silicon substrate. Usually, the spoiled units cannot be reworked. In the manufacture of high-precision machine tools, spoiled units can be reworked to meet standards, but only at a considerable cost. And in the mining industry, companies process ore that contains varying amounts of valuable metals and rock. Some amount of rock, which is scrap, is inevitable.