Even Further proving its mastery of chronographs and especially large-frequency precision, ZENITH unveils the DEFY El Primero 21 using a new El Primero calibre beating in a phenomenal level of 50Hz for an accurate one/one centesimal of a 2nd chronograph purpose. Thanks once more for choosing Watches World! We continue https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/