Seiko World Timers (6217-7000 (MASWT))
Stainless steel, 37mm. Twenty-four timezones represented by cities throughout the world are depicted on a bi-directional rotating inner bezel, which is accompanied by a day/night indicator bezel, and a distinctive auto-setting GMT hand. It originally came in two model variations, released only during the calendar year of 1964 in honor of the Tokyo Olympics: one variant with a silver dial, black/blue day/night indicator, white rotating 24hr timezone bezel, and black GMT hand; and one with a gray dial, silver/brown day/night indicator, black rotating 24hr timezone bezel, and tawny GMT hand.
These are my favorite travel companions.