Patek Philippe, Ref. 2540, early type automatic Cal. 12-600, rare square dial, 18-karat yellow gold, circa 1958. 

Ref. 2540 is a rare square design automatic 18k yellow gold model with the same case design as Ref. 2540, but with an automatic movement.  The rounded square case is one of the most original designs among vintage Patek Philippe watches, and it is a unique gem with the unique volume of the square design, equipped with an automatic movement despite its 32mm size. It is equipped with Patek Philippe’s first in-house self-winding movement, Cal.12-600AT. It comes with an archival document.