A global time clock displays the local times and dates of cities located in different time zones throughout the world. These clocks are commonly available on websites that chart or convert the current times of international metropolitan areas.
Global time clocks are used for a variety of purposes, such as worldwide communication, trade and business collaboration. These clocks operate through the scale of Coordinated Universal Time, which serves as an international reference for people contacting each other from separate time zones. Some global time clocks may be accompanied by maps to depict multinational time zones through projections that divide individual zones between marked borders. All time zones measure new days as beginning at midnight in order to keep global time synchronized with the earth's rotation.
Coordinated Universal Time replaced the former international standard of Greenwich Mean Time in 1972, the date global clocks were adjusted to measure International Atomic Time. Even though Greenwich Mean Time is no longer used as a basis in modern international timekeeping, the Greenwich Observatory remains the location of the Prime Meridian shared by global time clocks worldwide. Global time clocks additionally account for Daylight Saving Time adjustments used by different nations according to their observational traditions.