The Omega Reference 2639-12, with caliber 266, is a mid-century men's dress watch produced in the 1950s. Featuring a 36mm "Staybrite" (stainless steel) case, it typically sports a champagne or silver dial, sometimes with arrowhead markers and Dauphine hands. The manual-wind Caliber 266 movement is known for its reliability and simplicity, offering approximately a 45-hour power reserve and a frequency of 18,000 vph. This model includes a subsidiary seconds dial at the 6 o'clock position. The 2639 reference is valued for its classic design and wearability, often considered a "jumbo" for its era due to its relatively large 36mm case.