The Zenith movement introduced in 1969 as one of the first automatic mechanical chronograph calibres was El Primero.
Zenith developed El Primero during the 1960s, when several manufacturers were competing to create a self-winding chronograph. Its name means “the first” in Spanish, reflecting Zenith’s claim to an important place in that race. The movement was notable for its high frequency of 36,000 vibrations per hour, allowing measurements to one-tenth of a second.
El Primero was presented in 1969 alongside other early automatic chronograph systems, including the Chronomatic project associated with Heuer, Breitling and Bü ren. It later became especially important to Zenith because production of the calibre continued after the quartz crisis threatened many Swiss mechanical-watch manufacturers.
The name refers to the movement family, not one single watch model. Zenith has used the calibre in several watches, while other brands have also used modified El Primero movements.