Zenith?s El Primero automatic chronograph caliber ? unveiled to the world on this date in 1969 ? is regarded as one of the world?s best and most accurate movements. In this historical feature from our November-December 2017 issue, WatchTime contributor Thomas Gronenthal takes a look at its development.
 

It?s not uncommon for a watch to become a classic. But it?s much less common for a watch movement to gain fame and, after nearly 50 years, achieve legendary status.
In Switzerland, toward the end of the 1960s, two coalitions of watch manufacturers were hard at work developing the world?s first automatic chronograph movement. A leading role was played by Breitling, which collaborated with Heuer-Leonidas, Hamilton/Bu?ren and Dubois De?praz to develop a micro-rotor caliber that was unveiled simultaneously in Geneva, New York, Hong Kong, and Beirut in March 1969. In Japan, Seiko was working on its own automatic chronograph movement, Caliber 6139, which was introduced to the Japanese market in May 1969. But Zenith and its partner Movado had managed to publicly announce the development of an automatic chronograph movement and show a working prototype at a press conference in Geneva on Jan. 10, 1969, calling its new watch the ?El Primero? (meaning ?the first?). This movement?s technological victory march was almost impossible to stop. It measured 13.5 lignes in diameter and was a mere 6.5 mm tall. A dry lubricant based on molybdenum sulfate was used for the first time...