World Time Zones Map

Most countries have vary simple time zones with only one passing through their country. However, many countries have very complex time zones and time zone rules that even confuse the local residents. Some of the World's countries most complex time zone borders, setups, and rules include - Australia, Brazil, the U.S. state of Arizona, Russia, the Falkland Islands, small pockets of Canada, Greenland, Antarctica and the island nations(Kiribati, Marshall Islands) along the international date line.

The 24-hour clock is the format of time keeping in which the day runs from midnight to midnight and is divided into unique 24 increments, indicated by the hours passed since midnight, from 0 - 23. This simple time display format is the most commonly used time notation in the world today, and is used by international Data elements and interchange formats standard ISO 8601. In the theater of medicine, the 24-hour clock is generally used in documentation of care as it prevents any time errors as to when events occurred in a operation theater or patient's medical records. It is popularly referred to as “military time” in the United States, Canada, and a handful of other countries where the 12-hour clock is still mostly used by the Military.

A time-of-day format is written in the 24-hour notation in the display form hh:mm (for example 01:23:45) or hh:mm:ss (for example, 01:23:45), where hh (01) is the number of full hours that have passed since midnight, mm (23) is the number of full minutes that have passed since the last full hour, and ss (:45) is the number of seconds since the last full minute. Seconds are generally not used in 24 hour time display by most users. In the case of a leap second, the value of ss may extend to 60. A leading zero is added for numbers under 10. This zero is optional for the hours, but very commonly used in computer apps, where many specs require it (for example, ISO 8601).

Where sub-second resolution is required, the seconds can be displayed in a decimal fraction unit, that is, the fraction part follows a decimal dot or comma, as in 01:22:47.548. The most commonly used divide symbol between hours, minutes, and seconds is the colon, which is also the symbol used in ISO 8601. Recently, in the past, some European countries used the dot on the line as a divider, but most time national standards on notation have been changed to the international standard colon separator. In some usages (including the U.S. military and some computer apps and protocols), no separator is used and times are written simply as "2359".

The 12-hour clock format is a time display in which the 24 hours of the day are divided into two periods: A.M. ( or "before midday") and p.m. ( "after midday"). Each period consists of 12 hours numbered: 12 (acting as zero), 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11. The 24 hour/day cycle starts at 12 A.M., runs through 12 noon (often indicated as 12 P.M.) and at the end of the 24 hour period moves immediately to 12 A.M. of the next day. The natural day/night division of a calendar day forms the fundamental basis as to why each day is split into two time cycles. Originally these were one time cycle which could be tracked by the position of the Sun (day) followed by one cycle which could be tracked by the Moon and stars (night). This eventually evolved into the two 12-hour periods that started at midnight (A.M.) and noon (P.M.).

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