In the late 1960s there was a prestigious race to develop the world's first mechanical chronograph with automatic winding: Heuer-Leonidas and Dubois Dépraz had initiated the secret "Project 99" to develop such a movement, bringing in Hamilton/Büren and Breitling. On March 3, 1969, this group presented their product under the name of "Chronomatic" ​​simultaneously in Geneva, New York, Hong Kong and Beirut. The barrel of the Chronomatic is wound by means of an eccentric weight segment, a concept called a "microrotor".

Realizing that this announcement was imminent, Zenith rushed to preempt them. Their Cal. 3019 "El Primero" movement ("The First") was unveiled in a quiet press conference in Geneva on January 10 of the same year. They had begun developing their integrated automatic chronograph at the beginning of the decade, with the project stalled and restarted later. By late 1968, a few El Primero prototypes had been produced and these were shown to the world in January. It was not until late in 1969 that Zenith was able to produce customer-ready movements and watches. By this time, both the Chronomatic and Seiko 6139 were already in production and available to customers.