A color computer wheel includes a white base member upon which four concentrically arranged discs are rotatably mounted by a central fastener, the discs decreasing in diameter from bottom to top and being made of a transparent sheet material. The top disc carries four concentric annular bands, each evenly...http://www.google.com.tw/patents/US4399353?utm_source=gb-gplus-share專利 US4399353 - Color computer wheel
