These machines generally perform high-speed operations in which, one property of each piece of rock (physical or chemical) is measured by the sensor. Then the characteristic measured by the special algorithm and the computer decision is processed. If the output is finally accepted, that particle is chosen as a high-grade, otherwise it will be rejected as low-grade. The measurement characteristic can represent the element type, element grade, density, color, magnetism, etc. for detection, processing, and decision making.