Further Proving its mastery of chronographs and specially higher-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 one/100th of a next chronograph function. 1844: Adolphe Nicole introduces the reset element, allowing various times for https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/