Even Further proving its mastery of chronographs and especially substantial-frequency precision, ZENITH unveils the DEFY El Primero 21 having a new El Primero calibre beating at a phenomenal charge of 50Hz for an precise 1/a hundredth of the second chronograph purpose. The term “chronometer” took on a slightly broader meaning https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/