More Proving its mastery of chronographs and especially large-frequency precision, ZENITH unveils the DEFY El Primero 21 with a new El Primero calibre beating at a phenomenal fee of 50Hz for an exact one/one hundredth of the next chronograph operate. 1844: Adolphe Nicole introduces the reset attribute, making it possible https://www.watchesworld.com/understanding-the-complex-world-of-chronometers/