Further Proving its mastery of chronographs and particularly substantial-frequency precision, ZENITH unveils the DEFY El Primero 21 using a new El Primero calibre beating in a phenomenal charge of 50Hz for an correct 1/100th of the second chronograph function. Inspired by British pilot’s watches through the 1970s, Hamilton’s Khaki Aviation https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/