Optical electric system for use with measuring instrument

Claim 1

AN OPTICAL ELECTRIC SYSTEM FOR USE WITH A MEASURING INSTRUMENT INCLUDING IN COMBINATION A ROTATABLE MIRROR, A CONCAVE SCALE AND AN IMAGE PLANE, A SCREEN DISPOSED AT SAID IMAGE PLANE, MEANS INCLUDING A LIGHT SOURCE FOR PROJECTING A BEAM OF LIGHT BY WAY OF SAID ROTATBLE MIRROR ONTO SAID CONCAVE SCALE, SAID CONCAVE SCALE INCLUDING A REFLECTIVE SURFACE AND SCALE REPRESENTATIONS ON SAID REFLECTIVE SURFACE, SAID REFLECTIVE SCALE RETRODIRECTING THE LIGHT RAYS PROJECTED THEREUPON, AND MEANS PRODUCING AN OPTICAL SIGNAL ASSOCIATED WITH SAID CIRCULAR SCALE BUT SEPARATE FROM SAID SCALE REPRESENTATIONS, AN OPTICAL IMAGE FORMING ELEMENT PLACED ON THE OPTICAL AXIS OF THE SYSTEM BETWEEN SAID SCALE AND SAID IMAGE PLANE WHEREBY LIGHT INCLUDING THE OPTICAL SIGNAL IS RETRODIRECTED BY SAID CONCAVE SCALE BY WAY OF SAID ROTATABLE MIRROR AND THROUGH SAID OPTICAL IMAGING FORMING ELEMENT TO THEREBY FORM AN IMAGE OF AN ILLUMINATED PORTION OF SAID SCALE ON SAID SCREEN, MEANS INCLUDING A PLURALITY OF PHOTOELECTRIC CELLS DETECTING THE OPTICAL SIGNALS, ELECTRICAL CIRCUIT MEANS ASSOCIATED WITH SAID PHOTOELECTRIC CELLS INDICATING CHANGES IN THE POSITION OF THE ROTATABLE MIRROR.