However, the number of standard time zones is debatable and discussed among various sources, particularly with regards to the International Date Line. It is important to note that some countries have non-standard time zones, usually with a 30-minute offset (some have a 45-minute offset). For example, India maintains a time zone of five hours and 30 minutes ahead of Coordinated Universal Time (UTC+5:30).
The Greenwich Meridian, also known as the prime meridian or International Meridian, bisects the primary division of time zones. Each time zone is 15 degrees of longitude in width, with local variations, and observes a clock time one hour earlier than the zone immediately to the east.