Economics was behind the international agreement that divided the world into standard time zones 120 years ago. Until then, each country -- and often territories within countries -- used its own local time for business and transport schedules.
But an 1883 treaty designated the Royal Observatory in Greenwich, England, as the base position for a standard time system.
As more countries recognized the worldwide standard, they began referring to their own clocks in terms of hours ahead or behind "Greenwich Mean Time."
But the introduction of daylight-saving time during the summer months has complicated matters.
Those who participate move their clocks forward by one hour in the spring and back one hour in the fall. But not all places observe daylight-saving time: Neither Afghanistan's nor the former Soviet republics of Central Asia participate, for instance. So people who do business across time zones must keep track of multiple rules.
In Asia, where "offset" time zones are used, things are even more complicated.
Iran is a half-hour ahead of Iraq to the west and a full hour behind Afghanistan to the east.
But Afghanistan's is just a half-hour behind other neighbors. So when it is noon in Kabul, it is 12:30 p.m. in Turkmenistan, Uzbekistan, Tajikistan, and Pakistan.
Niklas Swanstorm is director of Contemporary Silk Road Studies at Uppsala University in Sweden. He says some insist on offset time zones because they think it implies national sovereignty.
"It's a political expression," Swanstorm says. "Simply that you want to state your national difference -- your national independence -- by being different. One of the case examples is Nepal, where it is just 15 minutes difference from India. That is ridiculous from anything else than a political point of view. When you are too close to another country, when you are too similar in a sense, you will find anything that makes you unique or different. And the time zone just might be one of these things."
Hooman Peimani is a Geneva-based independent consultant for firms doing business in Central Asia.
"Pakistan and Afghanistan are a totally different story," Peimani says. "There have been some problems between [Kabul and Islamabad]. To start with, Afghanistan does not recognize the borders as dictated to them. If there is anything, it is not because of geographic issues but because of political issues."
Just To Be Different?
None of the former Soviet republics of Central Asia uses an offset time zone. Uzbekistan, Turkmenistan, and Tajikistan all are five hours ahead of Greenwich Mean Time. Kyrgyzstan is six hours ahead of Greenwich. Kazakhstan has three time zones.
Peimani says Central Asia's time zones are based more on geography than politics.
"They want to be different from Russia," Peimani says. "That's a fact. And there are some political issues behind that. But beyond that, and as far as their relations with each other are concerned, at the time of independence [from the Soviet Union] it did not occur to anyone that they should have different time zones in order to secure some kind of political or economic objectives. This situation has been the case over the last century or so. The different time zones [of the former Soviet republics of Central Asia] are due to the geographical differences between these countries and I don't think there is anything beyond that."
Swanstorm argues that it would be more practical to create one time zone for all of Central Asia.
"It would make sense to change to a uniform Central Asian time -- simply because of the hour," Swanstorm says. "It makes much greater sense for the United States to have different time zones because the East Coast and West Coast work in different time zones. But the Central Asians don't really do that. In the region -- whether you like it or not -- there are lots of characteristics that are similar. And [the difference between the current Central Asian time zones] is such a small difference anyway."
But Peimani says Central Asia's economic problems should not be blamed on time differences within the region.
"It is due to a variety of things -- including not having much to offer to each other," Peimani says. "The main export of these countries is oil and gas. And for the rest, it is cotton. So in terms of interstate trade, they really do not have a lot to trade other than, perhaps, dried fruit and some kind of light consumer goods -- some kind of manufactured goods. So if they change the time zones, I think they can remove barriers to trade to the extent that one hour can create barriers. But beyond that, I don't think that by having one time zone for the entire region you are going to have a significant change in terms of trade or economic activity in the region."
Elsewhere in the world, the system continues to evolve because of economic concerns.
In the United States, daylight-saving time is four weeks longer in 2007 than in the past. That's because the Energy Policy Act of 2005 took effect there this year, pushing forward the start of daylight-saving time to the second Sunday of March (March 11) and extending it until the first Sunday of November (November 4).
The U.S. legislation aims to save 10,000 barrels of oil a day by reducing the use of power by businesses during daylight hours.