18ct yellow gold Patek Philippe, reference 2526 Calatrava automatic wristwatch. Made 1953

Launched in 1953, the Patek Philippe reference 2526 was the epitome of mid-20th century design with its oversized 35.5mm diameter Baumgartner-fabricated case.  The 2526 is Patek Philippe's first self-winding wristwatch consisting of an in-house 12-ligne movement, roughly 6 mm in diameter. The calibre 12-600AT features Patek's Gyromax balance wheel (first introduced in 1951), which is an adjustable inertia balance. A Gyromax balance's adjustment screws are not, as is usually the case, on the outside of the rim – instead, they are actually recessed into the rim of the wheel. Production continued until 1960 and during the 12-600’s seven year production period, 7100 movements were made and were featured not only in the reference 2526, but also in references as diverse as the 2540 to the 3425.