Additional Proving its mastery of chronographs and specifically higher-frequency precision, ZENITH unveils the DEFY El Primero 21 that has a new El Primero calibre beating at a phenomenal level of 50Hz for an accurate 1/100th of the next chronograph function. This was the result of intense R&D from the Manufacture, https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/