Table stopping device having null sensor

Claim 1

THE COMBINATION OF A RELATIVELY FIXED NULL SENSOR COMPRISING LONGITUDINALLY SPACED APART PHOTOSENSITIVE DEVICES, A TRANSVERSELY DISPOSED REFLECTIVE OBJECT THEREBETWEEN A PRISM SHAPE AND PRESENTING A BEAM SPLITTING KNIFE EDGE, AN ILLUMINATING BULB IN VERTICALLY SPACED APART CONFRONTING RELATION TO THE KNIFE EDGE OF THE PRISM AND DISPOSED IN THE VERTICAL PLANE OF THE PHOTOSENSITIVE DEVICES, AND AN INTERVENING, LONGITUDINALLY MOVABLE OPAQUE STRIP BETWEEN THE BULB AND PRISM, SAID STRIP CARRYING UPSTANDING BEAM-GUIDING TUBE MEANS ESTABLISHING COOPERATION WITH THE REFLECTIVE OBJECT WHEN PRECISELY IN THE VERTICAL PLANE OF THE KNIFE EDGE, WHEREBY THE CORE OF THE LIGHT BEAM SHINES SQUARELY ON THE EDGE SO AS TO PRECISELY SPLIT THE BEAM FROM SAID BULB EQUALLY BETWEEN THE PHOTOSENSITIVE DEVICES, SAID UPSTANDING BEAM GUIDING TUBE MEANS COMPRISING A PLURALITY OF EQUALLY SPACED APART TUBES CARRIED BY THE OPAQUE STRIP AND HAVING MEANS OF ADJUSTMENT WITH RESPECT TO THE STRIP SO THAT THE STRIP UNDERGOES PRECISELY UNIFORM AMOUNTS OF TRAVEL BETWEEN THE POINT WHERE ONE TUBE SHINES LIGHT SQUARELY ON THE EDGE AND THE POINTS WHERE EACH SUCCESSIVE TUBE SHINES THE LIGHT SQUARELY ON SAID EDGE.