Further More proving its mastery of chronographs and specially substantial-frequency precision, ZENITH unveils the DEFY El Primero 21 that has a new El Primero calibre beating in a phenomenal rate of 50Hz for an correct one/one centesimal of the next chronograph functionality. Influenced by British pilot’s watches with the seventies, https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/