Patent ID: 7607979

Claim:
A disk for identifying individual symbols on a reel displayed in a symbol display region of a mechanical slot machine, the disk comprising: a circular plate concentric, with the rotational axis of the reel and rotatable around the rotational axis together with the reel; and a plurality of members arranged on a surface of the circular plate and radiating outward from the rotational axis to distances that uniquely vary with the members, each of the members having a detection surface arranged on a corresponding circumferential surface of a radial tip thereof such that the detection surfaces of the members are located at circumferential positions relative to the disk that correspond to respective circumferential positions of the individual symbols on the reel; and a side surface extending in a radial direction between two of the detection surfaces adjacent to each other in a circumferential direction; the detection surface of each of the members being located at a unique radius relative to locations of the detection surfaces of others of the members such that the detection surfaces of the members provide reference to the individual symbols, the detection surface of each of the members being shaped with a specific pattern in which radial distances of portions of the detection surface from the rotational axis vary in a circumferential direction, and the detection surface of each of the members being configured to reflect ultrasonic or electromagnetic waves received from an external distance sensor in a radial direction such that the external distance sensor detects reflected waves from the detection surface of each of the members while the reel spins about the rotational axis, the detected pattern of the reflected waves corresponding to the specific pattern of the detection surface.