Further Proving its mastery of chronographs and specifically large-frequency precision, ZENITH unveils the DEFY El Primero 21 that has a new El Primero calibre beating in a phenomenal amount of 50Hz for an exact 1/a hundredth of a 2nd chronograph functionality. This was the results of intense R&D by the https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/