IWC Watch Portofino Perpetual Calendar Gold IW344602. The Portofino Perpetual Calendar features the legendary perpetual calendar developed by Kurt Klaus during the 1980s. At 40 millimetres, the Portofino Perpetual Calendar is the smallest perpetual calendar in IWC’s portfolio. This version features an 18-carat 5N gold case, a silver-plated dial, and gold-plated hands and appliques. IWC’s legendary perpetual calendar was originally engineered during the 1980s by the brand’s former head-watchmaker, Kurt Klaus.