This is an authentic Seiko Cronos (Ref. J13013), one of the most historically significant mechanical wristwatches produced by Seiko, manufactured in the late 1950s to 1960s era by Daini Seikosha (Kameido factory). Historical Background The Seiko Cronos occupies a crucial position in the history of Japanese mechanical watchmaking. First introduced in 1958, it was developed during a period when Seiko was internally divided between two major manufacturing philosophies: Suwa Seikosha and Daini Seikosha (Kameido). At the time, Suwa had already gained recognition with the Marvel, released in 1956—a highly accurate, robust hand-wound watch that set a new benchmark for domestic timepieces. In response, Daini Seikosha undertook the development of the Cronos as its first full-scale men’s mechanical wristwatch, marking a major turning point for the Kameido factory. Japan was entering a period of rapid economic growth, and wristwatches were increasingly demanded as reliable business tools. The Cronos was designed to meet this need, emphasizing practicality, legibility, thinness, and mechanical precision, rather than ornamental excess. Its clean dial layout, slim case profile, and restrained aesthetics reflect a clear design philosophy focused on daily usability. Technically, the Cronos incorporated advanced solutions for its time, including refined regulation mechanisms and a structurally stable balance system. Rivalry with the Marvel and Technical Philosophy The Cronos was developed under strong internal competition with Suwa Seikosha’s Marvel. While both models employed a traditional three-hand configuration, the Cronos distinguished itself through a thinner and more streamlined design, as well as a different mechanical philosophy. Unlike the Marvel’s cantilever-style balance, the Cronos adopted a double-supported balance bridge, improving stability and long-term accuracy. This structural choice clearly illustrates the contrasting engineering approaches between the two factories. This internal rivalry accelerated Seiko’s technological progress and ultimately led to the creation of later high-end models such as the Crown, King Seiko, and eventually Grand Seiko. Movement and the Significance of 23 Jewels The Cronos movement represents a crystallization of Daini Seikosha’s postwar technical philosophy. Its bridge design features gentle curves and a robust layout, balancing precision with durability and serviceability. This particular example is equipped with a 23-jewel movement, which is less common than the standard 21-jewel configuration. The increased jewel count was not merely cosmetic—it reflects Seiko’s effort to further reduce friction, improve longevity, and refine the overall mechanical efficiency of the movement. Rather than being a mass-production-oriented design, the Cronos movement retains a character that suggests careful engineering priorities and mechanical integrity. In this sense, the Cronos can be regarded as a developmental platform within Seiko’s broader technical evolution, bridging early postwar mechanical watches and later advanced designs. Condition and Operation As a vintage mechanical watch, this Cronos was running at the time of listing. The watch has been gently cleaned, and all functions operate as expected for its age. Please note: Accuracy and long-term performance are not guaranteed Water resistance is not guaranteed Service history is unknown These disclaimers are standard for vintage mechanical watches of this era. Summary The Seiko Cronos is not simply an old wristwatch—it is a historically important model that represents Seiko’s internal technological competition and innovation during a formative period of Japanese watchmaking. With its elegant design, refined hand-wound movement, and less-common 23-jewel configuration, this piece offers both historical depth and mechanical character for collectors who appreciate true vintage Seiko heritage. The watch will be carefully packed and shipped with tracking to ensure safe delivery.