The top-of-the-range model is the Ingenieur Perpetual Calendar Digital Date-Month (Ref. IW381701). The perpetual calendar automatically recognizes the different lengths of the months, including the leap day occurring every four years; it is extremely easy and convenient to adjust using the crown. The IWC-manufactured 89800 calibre also features a chronograph function. The timepiece with a 45-millimetre 18-carat red gold case, silver-plated dial, black hands and black alligator leather strap is limited to just 100 watches.