Within a couple of months of Basel 1969, Seiko released Cal. 6139, which utilized a new coupling system, developed and patented by Seiko, for engaging the chronograph, such that backlash is eliminated. It was a revolutionary idea--the world’s first fully-integrated automatic chronograph with a vertical clutch mechanism. And while Seiko 6139 may not have been the first to be announced, it was indeed the first to be available to the public by August 1969, beating both the Zenith El Primero and the Calibre 11/Chronomatic to the stores.
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