Additional Proving its mastery of chronographs and exclusively superior-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 accurate one/one hundredth of a 2nd chronograph function. Influenced by British pilot’s watches through the nineteen seventies, https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/