The Patek Philippe Calatrava Reference 3520 is a vintage dress watch known for its ultra-thin profile and classic aesthetic. Produced from the 1970s through the early 2000s, this reference is highly regarded for introducing the signature "Clous de Paris" (hobnail) bezel to the Calatrava line.

• Case: 32mm diameter 18k yellow gold with a thickness of approximately 5.1mm to 5.5mm.

• Dial: White porcelain or matte finish featuring black Roman numeral hour markers and blackened baton hands.

• Movement: Manually wound, ultra-thin caliber. Early models (1973–1977) typically used the Caliber 175, while later models used the Caliber 177. Both are derived from the Frederic Piguet 21 and measure under 2mm in height.

• Crystal: Scratch-resistant sapphire crystal (though some very early vintage examples may feature acrylic).

• Strap/Buckle: Typically paired with a black leather strap and an 18k yellow gold tang buckle.