Based on this system, on October 13, 1884, at the Meridian Conference in Washington, 25 nations, established the world time order GMT (Greenwich Mean Time). GMT because the mean local time of the Royal Observatory Greenwich was chosen as the international zero meridians.
Since the earth rotates around its axis, any line drawn from pole to pole would theoretically have been possible as a reference longitude (meridian). Greenwich was a purely political choice. The French had their problems – which is why they called the “meantime of Paris, delayed by nine minutes and 21 seconds” until 1911 GMT.
That time difference between the highest point of the sun in Greenwich and the highest point of the sun in Paris. Germany introduced the unified time determination in 1893. In practice, the time zones do not rigidly follow the meridian lines but also the political boundaries of states and natural boundaries such as mountains or rivers. On January 1, 1972, UTC was introduced as the international time standard. The basis for determining the UTC are measurements by atomic clocks,
What Did The First GMT Watches Look Like?
At the beginning of the history of the GMT watch like the rolex submariner, a rigid second-hour hand was mounted to display the second time zone, which constantly moved at a fixed distance from the local time. But with the introduction of summertime at the latest, it became clear that the rigid double-pointer system was unusable.
More modern designs made it possible to move the second-hour hand around the dial via the crown, thus independently of the time set. That was the hour of birth of the “world clock,” on which a freely chosen second time can be set separately from the local time. The Radiomir GMT (PAM00998) from Panerai also offers this pure form of two time zones on one dial and provides a day/night display at nine o’clock – integrated into the small second’s display.