The Calatrava has long been heralded as one of watchmaking’s most iconic watches. First produced in 1932 and now over 90 years old, it has gone through several changes over the decades. Perhaps one of the most surprising of those changes was in 1965 when Patek launched the ref. 3520 that we have here. Heralded as the thinnest waterproof watch, the ref. 3520 features a screw-down caseback with caseback tool indents that reveal its rather innocuous secret. Produced for almost 25 years, the ref. 3520 saw two variants across four metals, yellow, pink, white gold, and platinum. The first series ref. 3520 was fitted with the cal. 175 movement, which was based on a movement design by F. Piguet. In 1977, Patek Philippe began using the Geneva-sealed cal. 177 movement in the second series of ref. 3520 watches, which is what powers our example here. In 1968, Patek Philippe introduced the ref. 3520D as a braceleted version of the ref. 3520. This model continued to be produced for an extremely long time, until it was finally discontinued in 2008. Despite its age, the ref. 3520 remains a highly sought-after watch among collectors and enthusiasts. Its unique design and technical excellence make it a true classic in the world of horology, and a rather interesting reference from within the iconic Calatrava family.

Watch is in overall excellent condition. The yellow gold case shows light surface scratches, with a couple of small nicks visible on the lower left lug. The case back retains crisp hallmarks and stamps along with a well-defined circular finish. The clous de Paris bezel shows gentle wear to the outer row. The dial and hands remain near mint. It is fitted with a black leather strap and a gold-plated generic buckle. Comes with Patek Philippe pouch.

Heralded as the "flattest waterproof watch in the word" upon its release, the 3520 is a smartly designed vintage Calatrava that straddles the line between the past and modernity.