Times of Day for Two Cities in the Same Time Zone Are off by One Hour (265715)

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The basis of standard time throughout the world is called Greenwich Mean Time (GMT) or Universal Time Coordinated (UTC). Time zones are sometimes labeled by noting the number of hours that they differ from GMT. For example, the time zone for Washington, D.C., United States, can be referred to as GMT -5, because it is five hours behind Greenwich Mean Time.

Areas of the world that observe daylight savings time (DST) add an hour to the time of day to take advantage of extra sunlight. However, the time of the year an area observes DST is determined by the hemisphere in which it is located rather than the time zone.

For example, in the first part of the year Washington, D.C. observes DST and "spring forward", because it is located in the Northern hemisphere. On the other hand, Lima, Peru is in the Southern hemisphere and does not observe DST until the second part of the year. Even though these two cities are in the same time zone, GMT -5, the time of the day in each city can differ by one hour. The difference of an hour can also result when an area in a given time zone does not observe DST at all.

The Pocket PC accurately reflects the time of day and time zone for a city as well as whether a city observes DST. An example can be demonstrated by following these steps:

1. Open the clock on your Pocket PC.
2. Tap the flag in the upper left corner of the screen, and then tap Settings.
3. Tap the System tab, and then tap Clock.
4. In the Clock dialog box, tap Visiting and select Washington, DC (USA) as your visiting city. Notice the time zone is GMT -5 Eastern U.S.
5. Now select Lima, Peru as your visiting city.
   
   The time zone is still GMT -5, but instead of GMT -5 Eastern US, it is listed as GMT -5 Bogota, Lima. During this demonstration, you may also notice that the time of day between the two cities differs by one hour.