IWC Watch Portofino Perpetual Calendar Steel IW344601. 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 stainless steel case, a silver-plated dial, and gold-plated hands and appliques, marking the first time the perpetual calendar is available in stainless steel in the Portofino collection.