This is a fantastic piece of 1970s Japanese racing history- powered by the groundbreaking Seiko Caliber 6139, one of the world's first automatic chronograph movements! The immediate selling point is the movement's technical superiority- it features a Column Wheel and the revolutionary Vertical Clutch system, which allows the chronograph to start instantly without any shudder- a technology that ensures supreme accuracy and was later adopted by Rolex for the Daytona. The large, horizontally brushed tonneau case is pure 1970s style, giving the watch a substantial and aggressive wrist presence. The clean black dial with its prominent single sub-register and internal tachymeter bezel emphasizes the watch's tool-watch functionality. This reference is part of the sought-after Speed-Timer line, confirming its Japanese Domestic Market (JDM) origin and its direct link to Seiko's golden age of automatic chronograph innovation.