Zenith SA is a high-end luxury Swiss watch manufacture started in 1865 by Georges Favre-Jacot at the age of 22, in Le Locle in the canton of Neuchâtel. Zenith was purchased by LVMH in November 1999, becoming one of several brands in their watch and jewellery division. The CEO of the company is Aldo Magada, who replaced Jean-Frédéric Dufour in 2014.
Zenith has a long reputation for the quality and precision of their watches. It is one of few remaining Swiss watch manufacturers that still produce their own movements in-house.
The El Primero calibre, which was first released in 1969, though still produced today, was one of the first automatic chronograph movements and has a frequency of 36,000 alternations per hour (5 Hz). This high rate allows a resolution of 1⁄10 of a second and a potential for greater positional accuracy over the more common standard frequency of 28,800 alternations per hour (4 Hz). The El Primero was honoured with a 2012 release of the El Primero Stratos Flyback Striking 10th, limited to 1,969 pieces (in honour of the original 1969 release date), that housed the same 36,000 vph movement and a sub-dial measuring in tenths of a second to make a complete rotation every ten seconds.
For more Detailed Reference in our source : Zenith (Watchmaker) at Wikipedia
Photo 1 : Zenith Grande Chronomaster XXT, Quantième perpétuel
Photo 2 : Chronograph El Primero, first version 1970
Photo 3 : Inside of Zenith pocket watch c. 1900–1910