More Proving its mastery of chronographs and precisely large-frequency precision, ZENITH unveils the DEFY El Primero 21 with a new El Primero calibre beating at a phenomenal fee of 50Hz for an exact 1/one centesimal of the 2nd chronograph operate. This was the result of intense R&D with the Manufacture, https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/