Further Proving its mastery of chronographs and specially superior-frequency precision, ZENITH unveils the DEFY El Primero 21 having a new El Primero calibre beating at a phenomenal fee of 50Hz for an accurate 1/one centesimal of the second chronograph functionality. This was the result of intensive R&D by the Manufacture, https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/