In the mid-1970s, IWC decided to redesign the Ingenieur to give it a more "fashion-forward" look. With this new model, IWC aimed to emulate the success of one of its rivals. A few years earlier, Audemars Piguet had struck gold with the luxury steel sports watch, the "Royal Oak," designed by Gérald Genta. In response, IWC brought Genta on board (who also designed the steel Patek Philippe Nautilus) to redesign the Ingenieur, along with two other models: the Golf Club and Polo Club. These watches were part of what IWC called its Collection SL. IWC’s SL catalog from 1976/77 reveals that the SL designation originally stood for “Steel Line,” emphasizing the intention to create a luxury steel watch, inspired by the success of the Royal Oak. However, with the later inclusion of non-steel watches in the SL collection and the passage of time, the SL designation has come to be seen as meaning “Sports Line.” At hand, we have the reference 3506, where the "Jumbo" evolved into a "skinnier" version, with a 34mm case size and a cool, typical Genta-designed 3-row bracelet with a folding clasp that fits wrists up to 19cm. The showstopper here is the grey-ish "Graph Paper Dial" variant, featuring a date function and yellow tritium lume—so cool! The watch is powered by the automatic, gilted cal. 37521 movement, protected by a magnetic inner caseback. We think these variants of the Ingenieur are on the rise and currently a bit undervalued. Get in touch! Specifications: - IWC Ingenieur SL- Reference 3506- Serial 239XXX dating to the mid-1980s- 34mm steel case- Grey “Graph Paper” dial- Tritium lume- Integrated bracelet- IWC calibre 37521 automatic movement- Fully checked by our watchmaker- One-year mechanical warranty- Free worldwide FedEx Priority shipping