Additional Proving its mastery of chronographs and exclusively large-frequency precision, ZENITH unveils the DEFY El Primero 21 by using a new El Primero calibre beating in a phenomenal level of 50Hz for an exact 1/a centesimal of a 2nd chronograph functionality. Tudor’s Black Bay line is on fireplace with collectors. https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/