IWC Watch Ingenieur Perpetual Calendar 41 IW344903. The Ingenieur Perpetual Calendar 41 is the first stainless steel model to combine Gérald Genta’s visionary Ingenieur design with Kurt Klaus’ crown-operated perpetual calendar. The watch features a 41-millimetre case and integrated bracelet made of stainless steel, a blue dial, and rhodium-plated hands and appliques. Seamlessly integrated into the case via a middle-link attachment, the H-link bracelet with a butterfly clasp ensures excellent wearing comfort.