1. A SELF-WINDING WATCH WOUND BY AN OSCILLATING MASS COMPRISING: (A) A MOTOR SPRING AND A CONVENTIONAL CENTER WHEEL; (B) A GOING TRAIN HAVING CONVENTIONAL MEMBERS INCLUDING A FIRST AND A LAST MEMBER; (C) A DIFFERENTIAL DRIVEN BY SAID OSCILLATING MASS AND OPERATIVELY CONNECTED TO SAID MOTOR SPRING AND TO SAID TRAIN, SAID DIFFERENTIAL BEING DISPOSED AFTER SAID SPRING AND BEFORE SAID LAST MEMBER OF SAID TRAIN, SAID DIFFERENTIAL DIRECTLY DRIVING SAID GOING TRAIN AND SAID MOTOR SPRING; SAID DIFFERENTIAL HAVING A TRANSMISSION RATIO SUCH THAT THE SAME ACTS IN A REDUCING CAPACITY DURING THE WINDING OF SAID MOTOR SPRING AND IN A MULTIPLYING CAPACITY DURING THE DRIVING OF SAID GOING TRAIN BY SAID MOTOR SPRING SO THAT SAID SPRING WILL ABSORB THE DIFFERENCE BETWEEN THE ENERGY PRODUCED BY SAID MASS AND THE ENERGY CONSUMED BY SAID WATCH.