Further Proving its mastery of chronographs and especially large-frequency precision, ZENITH unveils the DEFY El Primero 21 which has a new El Primero calibre beating at a phenomenal level of 50Hz for an correct 1/a centesimal of the 2nd chronograph function. Chronographs — with their bezels, scales and sub-dials — https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/