In 1969, a group of Swiss watchmakers, including TAG Heuer and Zenith, collaborated to develop the first automatic chronograph. On the other side of the world, Seiko secretly created its own automatic chronograph simultaneously.
The Swiss won the race, but Seiko’s solo effort is arguably more impressive. It resulted in the caliber 6139, which powered the iconic Speedtimer.
Seiko has continued to innovate automatic chronographs ever since, and the modern evolution of the 6139 is the 8R46, found in contemporary automatic Speedtimer references.
Honorable Mentions
6R15/35/55 Auto-Manual
The 6R series is the more refined counterpart to the 4R series. These calibers are almost exclusively found in the Presage collection, with the Alpinist being the lone exception.
The major differences compared to the 4R calibers are a higher beat frequency of 28,800, halfway to the 36,000 Hi-Beat mark, and a longer power reserve of 70-72 hours. It also allows the wearer to wind the watch manually, along with its ever-present automatic winding.