This watch features a rare square case design (often referred to as the Monaco style in collectors), making it significantly less common and thus more easily identifiable and collectible. The movement is a core member of the automatic chronograph technology wave of 1969, renowned for its vertical clutch and column wheel structure, and is still considered a representative work of Seiko mechanical chronographs. ✦ Key Features: • Rare square case design (Monaco style) • One of the world's earliest families of automatic chronographs • Seiko automatic chronograph movement, vertical clutch + column wheel ✦ Condition: • Timekeeping and functions are all in normal working order. • All vintage watches show signs of age and use, and are therefore considered non-waterproof. 【Brand】SEIKO 【Model】6139-8020 【Movement】6139B Automatic Mechanical Movement 【Crown】Original Crown 【Case Diameter】40*42mm (excluding crown) 【Dial】Original Dial 【Strap】Original Steel Strap, Original Buckle. Can be worn up to 20mm. 【Condition】As pictured, please see photos for details. 【Remarks】Lightly press the crown to adjust the date. Press the crown harder to adjust both the day and date.