TIME ZONES
It was in 1884 that the International Meridian Conference in Washington standardized and adopted a universal 24-hour time beginning at midnight at the Greenwich meridian. Until then, each city had its own time, defined according to its precise longitude. Thus, when it was 12:00 00′ in Geneva, it was 12:01 36′ in La Chaux-de-Fonds and 11:44 59′ in Paris. Today these three cities are located in the same time zone and thus share the same time. This standardized time norm was therefore imposed by the development of industry, and of the railway in particular, in order to make train timetables understandable. This standardized time gave rise to watches simultaneously displaying the time of several chosen time zones, or all of them at once (world time / universal time).
As early as 1963, Greenwich observatory time (GMT Greenwich Meridian Time) was replaced by the UTC standard (Coordinated Universal Time (UTC)). This new reference base has been adopted by the majority of countries in the world. UTC is a time scale between the international atomic time (TAI), which is stable, but disconnected from the rotation of the Earth, and the universal time (UT), directly linked to the rotation of the Earth and therefore slowly variable. A modification of UTC is underway in order to eliminate the need for leap seconds. This should take effect as early as 2035.
This standardized Time (GMT then UTC) gave rise to watches simultaneously displaying the Time of one or several chosen Time zones, or all of them (World time / Universal time).
DUAL TIME ZONE (GMT)
Different mechanisms and types of Display make it possible to display, in addition to local time, one or even several selected time zones. The indication of the second time zone(s) is generally shown on a 24-hour basis or supplemented by a “day-night” indicator to avoid any confusion between daytime and nighttime hours.
WORLD TIME / UNIVERSAL TIME
It simultaneously displays the time of all 24 time zones. World time / Universal time generally consists of a Disc and a ring (or two rings) of Displayarranged concentrically. Each is divided into 24 segments. One is graduated with the 24 hours and the other displays the name of a reference city for each of the 24 time zones. The Disc or the ring (or one of the two rings) rotates in 24h and thus offers a simultaneous and immediate reading of the time in each time zone around the globe.
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