Electro-optical compass card wherein transmissive member has random patterns that repeat for particular rotational positions

摘要: Apparatus, such as a compass, for determining the positional relationship between two structures having limited motion therebetween is disclosed. The apparatus includes photoelectric array spaced from an illuminating or light source. and source are mounted to first structure member, example, compass housing. A second member suitable rotating disc mask thereon located so substantially block transmitted being received by array. mask, however, transmission areas of selected shapes, spiral, three lines. These transmissive result in illumination unique, random patterns individual elements each specific relative position member. Also included means read only memory (ROM) which has stored therein information correlating unique with position. In operation pattern on compared then provided display.