Yes, 1/10 is the anniversary of the press conference to announce the existence of the El Primero. However, it was my understanding that no prototype was shown and no Zenith automatic chronometer watches were release for public sale until the summer of 1969. Meanwhile, Seiko was selling the Ref. 6139 automatic chronograph in to the public in Japan beginning in May 1969.
"So what can we glean from our investigation into the great race of 1969? Some answers are easy: Zenith first introduced the automatic chronograph watch to the public, while Seiko鈥檚 watch was the first to appear on the market. And while Heuer and Breitling were close behind the others in production, they were probably the first to put a plan for such a watch in motion."
"The Great Race of '69" - Gisbert L. Brunner, WatchTime Magazine - December 2009, pp.102-113.
Since Seiko was first to market, by my definition (not everyone else's), they are the "El Primero" and Zenith was "El Segundo".
No question of which chronograph design was best, it's the one still being made.
And that's Zenith!
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