ZENITH | EL PRIMERO, REF SP 1301STAINLESS STEEL CHRONOGRAPH WRISTWATCH WITH DATECIRCA 1970

Dial: silvered vignetteCalibre: cal. 3019 automatic, 31 jewelsCase: stainless steel, screw-down backCase number: 7'07D'911Closure: stainless steel buckleDimensions: 37.5mmSigned: case, dial and movementAccessories: none

The El Primero was one of the first three automatic chronograph movements introduced in 1969, together with the Heuer calibre 11 and Seiko's calibre 6139. Zenith was the first brand to announce its automatic chronograph movement, Seiko the first to release it and Heuer the first Swiss manufacturer to do so. The production of the El Primero movement was halted in 1972 during the quartz crisis. Still highly regarded in the industry, it was resurrected in 1986 since it was chosen by Rolex as the base calibre for their first automatic Daytona models.