An analog-to-digital converting system with automatic gain control. One end of a flexible shaft, is connected to an output shaft of the engine and the other end of which is connected to a rotary shaft of the fan. A first sequence of stimuli of a first trial is displayed to the user. For example, when a 3 DCG image is displayed on two adjacent display surfaces of the plurality of display surfaces, the image is divided corresponding to the display surfaces, and the divided images are generated on the display surfaces by using a perspective method having one vanishing point. A slurry may be communicated through the shunt flow path, and a control device may be operated to isolate the slurry from being communicated to the ancillary flow path.