Launched in 1986 in around 400 examples, reference 25643BA was the first self-winding series produced tourbillon, as well as the thinnest and lightest ever made, weighing just 0.134 grams. The textured sunray design of the dial is derived from an ancient Egyptian relief and inspired by astronomical symbolism, with the tourbillon at 11 representing the sun and the eleven hour markers as the planets.