The Rolex GMT Master is a part of the Rolex Oyster Perpetual watch collection. The GMT Master was originally designed in 1956 to aid pilots who travel through multiple time zones.
A new model of the GMT Master came out in 1983 that features a sapphire crystal which cannot easily be scratched. This model was named the GMT Master II.
Production for the 16710 GMT Master II model ceased in 2007. The successor 116710LN was introduced at Basel world fair 2007 (same specification as the already in 2005 presented all-gold model 116718). The new model boasts the ceramic bezel, polished bracelet center links with Daytona type clasp, maxi dial and green 24 hour hand found on the 50th anniversary edition.
The GMT can display time in two different time zones and the GMT II in three. Using the additional "GMT" hand which completes a 24 hour cycle in a single rotation, the GMT (and GMT II) uses a bi-directional rotatable bezel marked zero to twenty three allowing for a second time zone to be displayed with the GMT hand pointing to the bezel hour. The GMT II allows the GMT hand to be set independently from the hour hand thus allowing a third time zone.
A compass bearing can also be taken using the red 24 hour hand (the 24 hour hand must be set to local, standard time, not GMT). When the watch is laid flat with the 24 hour hand pointed in the direction of the sun, the 12:00 marker on the dial will point to true north (not necessarily the same as magnetic north) in the northern hemisphere. In the southern hemisphere, the watch must be oriented overhead, and looked at from below for the movement of the 24-hour hand to trace the sun's movement. When this is done, the 12:00 marker on the dial will point to true south.
The 50th anniversary edition of the GMT Master II was revealed at BaselWorld 2006. This new model features a number of technical enhancements, such as Rolex's patented Parachrom hairspring as well as a larger Triplock crown. The new model also has several cosmetic improvements such as larger hands and a new bezel made of an extremely hard ceramic material which greatly resists damage and discoloration. The numbers on this bezel are filled with a fine layer of gold (the stainless steel version features a bezel that has platinum encrusted numbers), using a process of physical vapor deposition.