Optical symbol indicators

Claim 1

AN OPTICAL SYMBOL INDICATOR COMPRISING A PAIR OF SUPERIMPOSED ROTARY DISCS BEARING THE SYMBOLS TO BE INDICATED AND EACH HAVING A CLEAR APERTURE THEREIN, EACH OF SAID DISCS HAVING A SYNCHRONIZATION POSITION, MEANS FOR PROJECTING IMAGES OF SYMBOLS FROM ONE OF SAID DISCS WHEN THE OTHER DISC IS IN ITS SYNCHRONIZATION POSITION WHEREIN THE APERTURE OF ONE DISC IS IN ALIGNMENT WITH THE PROJECTION MEANS, RESPECTIVE D.C. PULSE-OPERATED STEP-BY-STEP MOTORS CONNECTED TO THE DISCS, SAID MOTORS EACH BEING OF A TYPE DRIVEN THROUGH SUCCESSIVE STEPS RESPONSIVE TO D.C. PULSES APPLIED THERETO, ONE MOTOR BEING POSITIONED TO BE DRIVEN BY A PULSE OF ONE POLARITY AND THE OTHER MOTOR BEING POSITIONED TO BE DRIVEN BY A PULSE OF THE OPPOSITE POLARITY WHEN THE DISCS ARE IN SAID SYNCHRONIZATION POSITIONS, YIELDABLE STOP MEANS ENGAGEABLE BY THE DISCS WHEN SAID DISCS ARE IN SAID SYNCHRONIZATION POSITIONS, A SINGLE PAIR OF COMMON LINE CONDUCTORS CONNECTED TO BOTH OF SAID MOTORS, MEANS TO NORMALLY SUPPLY D.C. PULSES TO SAID COMMON LINE CONDUCTORS OF SUFFICIENT STRENGTH TO DRIVE SAID DISCS THROUGH SAID SUCCESSIVE STEPS BUT INSUFFICIENT TO OVERCOME SAID YIELDABLE STOP MEANS, AND MEANS TO SUPPLY A PULSE THROUGH SAID LINE CONDUCTORS TO THE STEP-BY-STEP MOTORS WHEN THEIR ASSOCIATED DISCS ARE IN THEIR SYNCHRONIZATION POSITION OF SUFFICIENT STRENGTH AND PROPER POLARITY TO OVERCOME THE YIELDABLE STOP MEANS OF ONLY ONE OF SAID ASSOCIATED DISCS, WHEREBY TO ADVANCE THIS ONE DISC BEYOND ITS SYNCHRONIZATION POSITION.