Longines L2.937.4.72.6 Ultra-Chron Classic, ULTRA-CHRON CLASSIC, L2.937.4.72.6, automatic watch, Ø 40.00 mm, stainless steel., Date, self winding mechanical movement beating at 36000 vibrations per hour, with a monocrystalline silicon balance-spring power reserve up to 52 hours., Water-resistant to 5 bar, scratch-resistant sapphire crystal, with several layers of anti-reflective coating on both sides., Sunray silver dial., Stainless steel bracelet, with double security folding clasp with micro adjustment system., ULTRA‑CHRON, In 1968, LONGINES launched the Ultra-Chron Diver, the first dive watch equipped with a high-frequency movement. At the time, LONGINES had already established itself as a pioneer in high-frequency technology. As early as 1910, the winged hourglass brand created the first high-frequency timekeeping device capable of measuring 1/10th of a second. In 1959, LONGINES developed the first high-beat movement for a wristwatch, an observatory chronometer that set new records in terms of accuracy. The new Ultra-Chron is inspired by the aesthetic codes and professional diving features of the 1968 model. These chronometer-certified watches are powered by an exclusive LONGINES calibre equipped with a silicon balance-spring and resistant to magnetic fields.