The Rolex GMT Master has the normal second, minute and hour hands and the date, and in addition a revolving bezel, calibrated into 24 hours and a red 24 hour hand.
Consequently it may be used to tell the exact time at any two places on the earth at once.
The red 24 hour hand revolves once around the dial every 24 hours and is directly connected to the normal hour and minute hands and moves with them, either during the normal runningof the watch or when the hands are being set.
The G.M.T. Master is easy to read if it is remembered that the normal hour hand is read on the dial and the red 24 hour hand is read on the revolving bezel outside the dial.
Suppose it is 2 o’clock in the afternoon in London and it is required to set the GMT Master to show London time and date and New York time. The London time and date are set first, using the normal hands, as described under “Setting to the second” and “Setting the date”.
When this has been done and with the 24 hour position triangle of the revolving bezel in a position corresponding to 12 o’clock on the dial, the red hand will read 14.00 hours-it, too, shows London time.
Knowing that New York time is five hours behind London time turn the bezel 5 hour markings in a clockwise direction. The red hand now reads 09.00 hrs. on the bezel New York time. The minute and seconds hands apply, of course, the both places.
For places west of Greenwich, the bezel must be turned in a clockwise direction. For places east of Greenwich, in an anti-clockwise direction.
Thus, having set the GMT Master to GMT or other “home” time, and date, on the dial as for a normal date watch, it is a simple matter to set the bezel to the other required time, knowing the number of hours it is ahead or behind GMT or “home” time.