Further More proving its mastery of chronographs and exclusively significant-frequency precision, ZENITH unveils the DEFY El Primero 21 having a new El Primero calibre beating in a phenomenal price of 50Hz for an accurate 1/a centesimal of the 2nd chronograph function. Impressed by British pilot’s watches through the nineteen seventies, https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/