Pictured here is one of my recent guests, straddling the Greenwich Meridian in Greenwich, England (at 0 degrees longitude and 180 degrees latitude) The Greenwich Meridian (Prime Meridian) marks the starting point of every time zone in the world. Greenwich Mean Time (GMT) is at the center of the time zone map. GMT sets current time or official time around the globe. Imagine the earth being split by North/South (the Equator) and by East/West (the Prime Meridian).
Before leaving , we all consulted with the most reliable clock in the world and re-set our watches with the cetainty of having complete accuracy.