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Before the end of the 19th century, there was no such a notion as “world time” since time keeping was a strictly local thing. Each community used to set their clocks to noon every day, with a town clock showing the official time. Mobile clock setters were people who had a watch with the accurate time and set the clocks in client’s homes once a week. Those who traveled between towns had to change their pocket watches after getting to their destination.

However, with the emergence of railroads, the issue of time became burning. The train schedules caused much confusion due to each stop having being based on a different local time. It was Canadian Sir Sanford Fleming whose suggestion to implement a brand-new system of world time zones was accepted by delegates from 27 nations in 1878 to ensure efficient operation of railroads. However, the Italian mathematician Quirico Filopanti outlined a similar system of world time zones a bit earlier, in 1858.

According to Fleming’s plan, the world is divided into twenty-four time zones, each 15 degrees wide. As it takes 24 hours for the Earth to make a spin on its axis and there are 360 degrees of longitude, each hour it rotates 1/24 of a circle or 15 degrees of longitude. The prime meridian time zone in Greenwich, England, is 180 degrees apart from the International Date Line drawn in the Pacific Ocean, where date changes to the following day.

This system appears to be much easier than the older system of using only local time. Most adjacent towns use the same time zone settings. Even in case they are situated in different time zones, the time settings differ by a whole number of hours, which makes the conversion from the time in one time zone to the time in the other one rather convenient.

Since time zones are set by delineating a straight line between the Poles, in some cases the time line divides a small town, thus placing one side of the town in one time zone and the other in a different zone.
No one can argue that the idea of strict time zone application is brilliant, but it can often be impossible and in many locations the lines are getting blurrier and blurrier inside one community to let all the residents live according to the same time. Such borders are usually shown on maps of world clocks and it is possible to see how many of the lines have widened or shrinked to let the time zone cover the whole town for avoiding confusion.

Nowadays, this world time zone system, significantly adjusted by state, provincial, or county boundaries, is used by most countries. It is important to understand that time zone lines are not set in stone. They change according to political developments. Here are a few practical examples as of the moment of this writing (April 2010).

Russia has changed its time zone map from 12 times zone to 10 in 2010.
China is, perhaps, the most extreme example. China uses one time zone (Beijing time) for the entire country but this may change.
Many small towns, and even small countries like Sri Lanka, occasionally tend to use the time zone and DST as of their larger neighbors. For example, Sri Lanka started to use India time zone in 2006. Mexican cities bordering USA switched to USA DST rules in 2009. Mexican communities in Nayarit, Mexico that are close to Puerto Vallarta, Jalisco switched to Mexico City time zone to be aligned with Puerto Vallarta time in 2010.

Time zone changes like this happen all the time. Therefore, the world time map is dynamic. It needs to be adjusted when changes occur.

World Time Clocks

A world clock, also called a world time clock, is a clock which displays the time for several or all time zones of the world.

In these days of a high-technology environment, constant travel and international business, the usefulness of world time clocks cannot be doubted. World clock makes it possible to decipher the time zone changes with a push of a button. For too many categories of people knowing what time it is in their time zone simply isn't enough and they need to know the current time in some other places of the world. Companies with affiliates and partners all over the globe particularly find world time clocks indispensable. Thus, businessmen may worry when they find it impossible to reach a customer half way around the globe until they check world clocks and discover there is a 12-hour time zone difference.

Types of Traditional World Clocks

There are numerous types of world time clocks which differ by the information they provide. As a rule, large hotel halls and airport offices have several clocks that show the time in such megapolises as New York, London, Berlin, Paris and Tokyo. One can also buy various kinds of sophisticated wristwatches or that display current time in two or more time zones chosen by the wearer. Usually these times are not on constant display, and it takes just a minor adjustment to see the time in Beijing or Moscow, while the wearer is, for example, in Milan. The world time zone clocks are very convenient and they generally consist of dials that are rotated.

International Time Zone Clocks constitute the category of clocks, which employ one display for all time zones. Some of them have an LCD and a keypad for choosing the time in a certain time zone, others use a movable dial. You can also find a world clock with full world map displaying every time zone, a day date calendar, and the changes in light pattern which shows the sun-lit part of the planet.

Time Zone Display Wall Clocks are separate clocks of various sizes and materials that can be placed on a wall with the labels of location names.

Multiple Time Zone Digital Clocks, powered by 110V or 220V current, have red or green LED numerals and show the local time in a number of places at the same time (commonly, up to eight).

In addition, there are Multiple Time Zone Wall Clocks and Desk Clocks which also serve the purpose of displaying the time in many locations simultaneously.

World Clock Software

However, the most popular world clocks of modern times are on the computer. As the Internet is gradually becoming an inseparable part of our lives, one can get synchronized with public servers across the world and know the current time in different places at the same time.

World clock software allows the users to know the current time in a certain time zone instantly by simply clicking a mouse button or key on the keyboard.

Software world clocks have an advantage over traditional world clocks by being able to adapt quickly to time zone and DST changes throughout the world via a software update mechanism. For example, if a time zone change occurs in some country, or daylight saving time is introduced, changed, or eliminated in a particular location, the change automatically propagates into software-based product as soon as manufacturer integrates it. You don't need to do anything.

Various types of the world clock software are bound to be further improved with additional features according to the user requests. For example, Anuko World Clock provides timers and stopwatches for different time zones, alarm system, time converter for easy calculations of overlapping work hours between locations, calendar, location-sensitive photo content, and more.