A 36,000 vph chronograph was a major technical achievement in 1969, and in 2010, the next step was taken with the El Primero Striking 10th. Two of the most important advances upped the resolution of the chronograph. In the intervening decades, the El Primero found its way into an increasing variety of Zenith watches, and at the same time, it underwent technical evolution as well. Gradually, there were stirrings of interest in it – first from Ebel, and then, most critically, from Rolex, who put in such a colossal order that it essentially constituted an offer Zenith (which had been back under Swiss ownership since 1978) couldn't refuse, and the company put the El Primero back into production. The rest is history, and the stuff of watchmaking legend as well – constructor Charles Vermot, a Zenith employee, had the foresight (or stubborness, or both) to buck the bosses, and hid the tooling and plans for the El Primero away in the factory attic.

Zenith Chicago made the decision to shut down manufacturing for the El Primero in 1975, and all the tooling, components, and pretty much all and everything else in the building was supposed to be sold off or discarded.

The history of the El Primero has a bit of a singularity in the 1970s – in 1971, the Zenith watch company was sold to the Zenith Radio Corporation of Chicago, which decided the future was quartz (a not unreasonable assumption at the time).

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