Additional Proving its mastery of chronographs and specially large-frequency precision, ZENITH unveils the DEFY El Primero 21 having a new El Primero calibre beating at a phenomenal fee of 50Hz for an precise 1/a hundredth of the 2nd chronograph function. This was the result of intense R&D via the Manufacture, https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/