World time

A world time watch (sometimes referred to as a worldtimer) is a visual and technical solution for simultaneously telling the time in 24 time zones around the globe in relation to local time. More often than not, these time zones are represented by a major city or place within the zone in question. Over the years, the majority of brands have adopted the same references. They are London (GMT), Paris (GMT+1), Istanbul (GMT+2), Moscow (GMT+3), Dubai (GMT+4), Karachi (GMT+5), Dhaka (GMT+6), Bangkok (GMT+7), Beijing (GMT+8), Tokyo (GMT+9), Sydney (GMT+10), Nouméa (GMT+11), Auckland (GMT+12), Midway (GMT-11), Hawaii (GMT-10), Anchorage (GMT-9), Los Angeles (GMT-8), Denver (GMT-7), Mexico (GMT-6), New York (GMT-5), Santiago (GMT-4), Rio (GMT-3), South Georgia (GMT-2) and Azores (GMT-1). Add to this the 13 countries whose time zone is offset by less than one hour, such as Nepal (GMT+5.45) or Venezuela (GMT-4.30), and this brings the total number of time zones to thirty-seven.

A world time display is structured around three concentric components: a 24-hour disc, a cities disc and a day/night indicator. Using an additional pusher (or in some cases the crown), the wearer rotates the city disc until the local city aligns with a fixed pointer at 12 or 6 o'clock. At the same time as the city disc is turned, both the hour hand and the 24-hour disc move in one-hour increments.

The day/night indicator can take several forms. The simplest solution is to divide the 24-hour disc into two differently coloured halves: white between 6am and 6pm for daytime and black between 6pm and 6am for night-time. A more sophisticated interpretation of recent years is the addition, in the centre of the dial, of a planisphere seen from above one of the poles (usually the North Pole), engraved on a sapphire crystal disc. Placed underneath, a second disc with light and dark shading rotates with the 24-hour disc to indicate daytime and night-time at different points around the globe, through the transparent crystal.

How does a world time display work? Hours and minutes for local time are set by the crown. The hour hand and the 24-hour disc are directly connected and rotate at the same speed, in the same direction if the 24-hour disc has anti-clockwise graduations and in opposite directions if it has clockwise graduations. The day/night indication always follows the rotation of the 24-hour disc. The city disc and planisphere, if there is one, remain static once correctly positioned.

On a few exceptional watches, the central planisphere is replaced by one (possibly even two) three-dimensional hemispheres. Some have the 24-hour scale rotate around this dome; on others, the dome turns on itself.

Whatever the chosen solution, a permanent indication of all 38 time zones on a mechanical watch is a highly complex endeavour. Firstly because, as seen, some parts of the world have chosen to offset their time by less than a full hour, and secondly because these changes are relatively frequent: a country has a sovereign right to determine its own local time. Not forgetting that not all countries in the world observe daylight saving time.

The earliest clocks, in the fourteenth century, were set by the only reliable reference at that time: a sundial. Therefore each community, each region had its own solar time that differed from that of a neighbouring community, even when the two were only a few miles apart.

In 1705 Johann Baptist Homann (1664-1725) devised the ancestor of today's world time watch: a world time clock that was later built by Zacharias Landeck (1670-1740). Circa 1780 makers such as Rouzier & Melly in Geneva were producing double-sided watches known as geographic watches. The time for the reference city was shown usually on the front dial by hands. On the reverse side, a central disc rotated anti-clockwise once in 24 hours to indicate local time in 53 cities and locations around the globe. The names of these cities were inscribed on a peripheral ring. In 1856 Modeste Anquetin (1817-1909) of France filed a patent for a double-sided watch. One side showed the hours, the other the minutes in various cities worldwide. However, Anquetin was ahead of his time and his invention failed to elicit any great interest. Come the late nineteenth century, certain world time watches were capable of displaying the time in 140 cities and places, including the main stations along the route of the Trans-Siberian railway.

The Industrial Revolution of the nineteenth century brought the expansion of the railways and an intensification of trade, making clear the need for a unified time. In 1840 the newly invented electric telegraph was tested on a section of the London-Blackwall line, sending the exact time to stations along the route. In 1883 the American and Canadian railroad companies agreed to divide their territory into five "time zones". At the International Meridian Conference in Washington the following year, 25 countries voted to divide the globe into 24 one-hour time zones, measured from the prime meridian in Greenwich.

It would, however, take a further fifty years and the first transcontinental telephone call for the world time function to come into its own. The first to attempt such a mechanism was Emmanuel Cottier (1858-1930) of Geneva, a maker of watches and automata. His son, Louis Cottier (1894-1966), would propose his own version in 1935, which he showed to Baszanger, a jeweller in Geneva. The younger Cottier's mechanism showed the time in 29 cities around the globe, initially on a pocket watch and soon after on a wristwatch. It wasn't long before he was supplying such prestigious names as Patek Philippe, Rolex, Vacheron Constantin and Cartier. Patek Philippe launched its own world time chronograph in 1940, based on a Cottier movement. It was followed by Breitling's Unitime (1951), Tissot's Navigator (1953), the Memovox Worldtime by Jaeger-LeCoultre (1959) which combined world time with an alarm, and the Edox Geoscope (1971). In 1990 the Géographique by Jaeger-LeCoultre became the first watch to show dual time and the time in 24 major cities worldwide.

After presenting a worldtimer in 1990 to commemorate Cottier's landmark invention, in 1994 Svend Andersen of Andersen Genève introduced the Mundus, the thinnest world time watch ever at 4.2mm high. In another world-first, Greubel Forsey's GMT (2012) features a three-dimensional globe on its dial. A second time zone is shown on the front, with a rotating world time city disc on the back. A number of brands would take up this trend, such as Montblanc and its Villeret Tourbillon Cylindrique Geosphères Vasco da Gama (2015) or Bovet Fleurier with its Recital 18 The Shooting Star (2016).

Also introduced in 2012, Glashütte Original's Senator Cosmopolite took a slightly different approach. Inside two apertures at 8 o'clock, cities in 38 time zones are designated by the IATA code for their main international airport: FRA for Frankfurt, CDG for Paris Charles de Gaulle, LHR for London Heathrow, JFK for New York, LAX for Los Angeles, PEK for Beijing, HND for Tokyo, etc.