Longines Watch Ultra-Chron Bracelet L2.836.4.52.6. Inspired by the original Longines Ultra-Chron Diver of 1968, the new model and its new high-frequency calibre represent the first reinterpretation of what sets Longines apart – its status as a pioneer in the world of sports timing. It will appeal to both vintage watch aficionados and lovers of high technology. The accuracy of the Longines Ultra-Chron is confirmed by its certification as an “ultra chronometer” by TIMELAB, an independent testing laboratory in Geneva. This designation goes beyond the usual “chronometer” certification.