The reason the world clock starts in Greenwich, England is because during the 19th century, the majority of sea charts used Greenwich, England as the Prime Meridian for the 0° coordinate. In addition to this, during the early advent of the British railway network, trains could end up in accidents if the timing of coming into and/or out of stations was off by even a small margin of error. Because the sun rises earlier in some parts of Britain and later in the rest, these variables needed to be compensated for which was accomplished by introducing more accurate clocks and the concept of time zones. Up until this point, horsepower was the fastest way to travel and because of that, sundials which had been invented in and used since the 9th century A.D., were satisfactory. It was only with the emergence of locomotives that this system of time keeping became antiquated