From the various tests carried out in the 1940s, it emerged that one of the methods of counteracting jet lag was to possess an instrument that would simultaneously indicate both the time zone of the place of departure and that of the flight's destination. Pan-Am, the former U.S. flag carrier, was among the first to meet this need, entrusting Rolex with the creation of a watch equipped with the specifications needed by pilots. Rolex then introduced the GMT Master model, equipped with a rotating bakelite bezel and a hand to mark the dual time zone. The present model 16700 is an evolution of the first reference 6542 and the susequent 1675, unlike the latter in this model Rolex introduced the sapphire crystal that was much more resistant to scratches