The El Primero was the culmination of a years-long research and development process undertaken by Zenith to develop the world’s first automatic chronograph movement. 

Zenith announced the El Primero at a press conference on January 10, 1969. This was four years later than Zenith had intended —the brand had begun developing the caliber in 1963, hoping to bring it out for Zenith’s centennial in 1965. Nevertheless, on that winter day in 1969, Zenith proudly displayed a working model of its chronograph. And the rest, as they say, is history. 

Fast forward to the 1990s, and Zenith was once again pushing the limits of what a contemporary chronograph could be and do. The company combined the El Primero’s impressive automatic movement with flyback capabilities, allowing the wearer to instantaneously reset the central chronograph seconds hand to zero and begin timing a successive event with the push of a single button. The resultant watch, dubbed the Zenith Rainbow, was a special commission for the French armed forces. 

In the early 2010s, Zenith adopted this technology to a civilian timepiece, which it dubbed the El Primero Stratos Flyback Striking 10th. Combining the flyback movement El Primero 4057 (an evolution of the Rainbow’s caliber 405) with a 1/10th-second chronograph feature that whips the second hand around the dial once every 10 seconds — plus a tri-color dial recalling the El Primero watches of the 1960s and 1970s — it represented the culmination of all Zenith had developed in automatic chronograph technology up to that point in time. 

This particular El Primero Stratos Flyback Striking 10th is housed in a 45.5mm stainless steel case with a sapphire crystal, a signed crown, ‘doorstop’ pushers, and a black ceramic unidirectional count-up bezel. It features a sunburst silver and black dial with applied indices, a  matching ‘sword’ handset, a date window above 6 o’clock, and a tri-color, triple-register chronograph layout in blue, brown, and grey. Powered by the automatic Zenith El Primero Calibre 4057, it’s paired to a stainless steel multi-link bracelet with a signed, push-button deployant clasp. What’s more, it’s in mint condition with its factory stickers intact, and ships with its factory goodies.