Maker: Patek Philippe
Model: Calatrava
Reference number: 2526J
Movement number: 766480
Case number: 2606828
Year: Circa 1950s
Case size: Approx. 36 mm
Case material: 18K yellow gold
Dial: Silvered
Movement: Automatic
Bracelet/Strap: Brown leather
Functions: Small seconds
Stamps: Inner case back: PATEK PHILIPPE & Co. GENEVE SWISS 18K 0.750 (Swiss hallmarks) 2606828 2526. Movement: PATEK PHILIPPE GENEVE No 766480 THIRTY (30) JEWELS.
Gross weight: 36.70 dwt.

The Patek Philippe Reference 2526J in 18K yellow gold is widely regarded by collectors as one of the most significant "time-only" wristwatches ever produced. Launched in 1953, it was the brand's first serially produced self-winding (automatic) watch and remains a cornerstone of mid-century horological design. 
It debuted the Caliber 12-600 AT, Patek's first self-winding movement. Patek spent decades perfecting this caliber while waiting for Rolex's 20-year patent on full-rotor mechanisms to expire in 1951.
While approximately 7,100 of these movements were made, only an estimated 580 to 600 examples of the Reference 2526 were produced across all precious metals.
The "J" suffix stands for jaune (yellow gold), which is the most common metal for this reference. Other versions include rose gold (R), white gold (G), and platinum (P).