Further Proving its mastery of chronographs and especially large-frequency precision, ZENITH unveils the DEFY El Primero 21 with a new El Primero calibre beating in a phenomenal price of 50Hz for an correct one/a hundredth of the second chronograph purpose. 1844: Adolphe Nicole introduces the reset function, enabling distinct periods https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/