https://wornandwound.com/chronograph...seiko-citizen/
Seiko 613X
I’ll begin with the 613x family from Seiko Suwa. There are two primary calibers: the earlier 6139 introduced in 1969 (and produced until approximately 1977), and the 6138 introduced a year later in 1970. The difference between the two movements is that the 6139 only has a 30-minute chronograph register, and the 6138 has an additional 12-hour register. Both lack an active running seconds and in terms of specs, they beat at 21,600bph and have a power reserve of 45 hours. Both also have a day/date indicator. The 6139 has 17 jewels, and the 6139 has 21 (and 23 for some of the rarer Japanese domestic market variants like the 6138-8000). Both variants lack hacking and the 6139 does not hand wind. In terms of size, the 613X is 27mm in diameter and 7.2mm (6139)/7.9mm (6138) tall.
SEIKO 6138 8020 “PANDA.”
The 613X family has numerous claims to fame, particularly the 6139. Alongside Zenith and the Chronomatic partnership, Seiko is widely acknowledged to be among the first companies (and some might even argue that Seiko was the first) to have an automatic chronograph watch out on the market. Peculiarly, this achievement was never marketed by Seiko nor given any mention in the official Seiko history, “A Journey in Time: The Remarkable Story of Seiko.” One fact that cannot be argued, however, was the Seiko was certainly the first Japanese watch company to produce and release an automatic chronograph.
Incidentally, the 6139 is also the first automatic chronograph sent to outer space, worn on the wrist of US astronaut Willian Reid Pogue during the 1973 Skylab-4 mission. This particular iridescent yellow-dialed model has now been nicknamed the “
Pogue.”
https://thespringbar.com/blogs/guides/the-seiko-6139-600x-collectors-guide/
Seiko can also claim the honor of having sent the first self-winding chronograph into outer space. When U.S. astronaut William Reid Pogue flew aboard the Skylab-4 mission in 1973 to 1974, he wore a watch (nowadays nicknamed the “Pogue Seiko”) powered by Caliber 6139.
https://www.pressreader.com/usa/watc...82080571022740
https://adventuresinamateurwatchfett...k-chronograph/