The 6139 entered serial production in January 1969 and reached stores that May, which puts it squarely in the most argued-over year in horology: the three-way race between Zenith's El Primero, the Swiss Chronomatic consortium's caliber 11, and Seiko's 6139 to be the first automatic chronograph. Who won depends entirely on how you define finishing, announcement, production or availability, and the file records the race rather than the winner.
What is not disputed: the 6139 was a column-wheel, vertical-clutch automatic chronograph with a quickset day-date, sold at a fraction of Swiss prices, and produced essentially unchanged for a decade. The first-run 6139-6000 and -6001 cases are where that history physically lives.
The race artifact. Early examples with the earliest dial variants carry the premium, and the family's parts interchangeability makes era-correctness the entire question: an early case wearing later service parts is a common watch with an uncommon story attached. The serial decoder and the dial details settle it together.
Production windows and specifications compiled from documented collector references and period catalogs, cross-checked across independent sources; manufacturer records for this era are approximate by Seiko's own account.