Further Proving its mastery of chronographs and especially significant-frequency precision, ZENITH unveils the DEFY El Primero 21 with a new El Primero calibre beating at a phenomenal price of 50Hz for an correct one/one hundredth of the 2nd chronograph operate. The expression “chronometer” took on a rather broader meaning as https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/