The invention concerns a watch equipped with means for determining a location longitude and a device for determining the sun's altitude above the horizon. Said watch comprises a mobile element (16) doing one full rotation in 12 hours and bearing a hour hand (24), and a dial (32). It comprises for this purpose a rotating ring (44) for reading longitude, bearing an index mark (47) and, therefrom, a scale (45) in degrees, extending from 0 to 90 on either side of the index mark and covering the ring (44) over its whole periphery. Moreover, the dial (32) is provided with a circular scale (33) for selecting a time zone, with a median point (35) corresponding to the dial top point and a graduation from 0 to +6 hours or -6 hours depending on the rotational direction.