Electric differential counter

Claim 1

AN ADD SUBTRACT DEVICE, HAVING IN COMBINATION, A HOLLOW SHAFT, A BEVEL GEAR FREELY ROTATABLE STEPWISE ON SAID SHAFT, ADD STEPPING MEANS ADAPTED TO ROTATE SAID BEVEL GEAR ONE STEP AT A TIME, A SECOND BEVEL GEAR FREELY ROTATABLE STEPWISE ON SAID SHAFT, SUBTRACT STEPPING MEANS ADAPTED TO ROTATE SAID SECOND BEVEL GEAR ONE STEP AT A TIME IN THE OPPOSITE DIRECTION, PINION ARM MEANS MOUNTED ON SAID HOLLOW SHAFT FOR ROTATING SAID SHAFT, BEVEL PINION MEANS ENGAGING BOTH OF SAID BEVEL GEARS AND SUPPORTED BY SAID PINION ARM MEANS WHEREBY ROTATIONAL MOVEMENT OF SAID BEVEL PINION MEANS BY SAID BEVEL GEARS WILL BE TRANSMITTED TO SAID HOLLOW SHAFT BY SAID PINION ARM MEANS, A CAM CARRIED BY SAID HOLLOW SHAFT, AN ELECTRIC SWITCH ACTUATED BY SAID CAM, A SECOND SHAFT EXTENDING THROUGH SAID HOLLOW SHAFT, A CAM CARRIED BY SAID SECOND SHAFT, AN ELECTRIC SWITCH ACTUATED BY SAID SECOND CAM, CLUTCH MEANS ENGAGEABLE TO RELEASABLY SECURE SAID TWO SHAFTS TOGETHER FOR PREVENTING RELATIVE ROTATION OF ONE SAID SHAFT WITH RESPECT TO THE OTHER, AND MEANS SECURED TO SAID SECOND SHAFT FOR DISENGAGING SAID CLUTCH MEANS WHEREBY THE ANGULAR RELATION OF SAID SHAFTS AND THEIR ATTACHED CAMS MAY BE CHANGED.