Each railroad used its own standard time, usually based on the local time of its headquarters or most important terminus, and the railroad's train schedules were published using its own time.
For example, Bristol is about 2.5 degrees west of Greenwich (East London), so when it is solar noon in Bristol, it is about 10 minutes past solar noon in London.
The use of time zones accumulates these differences into longer units, usually hours, so that nearby places can share a common standard for timekeeping.
The zones were named Intercolonial, Eastern, Central, Mountain, and Pacific.
Within a year 85% of all cities with populations over 10,000, about 200 cities, were using standard time.
Before clocks were first invented, it was common practice to mark the time of day with apparent solar time (also called "true" solar time) – for example, the time on a sundial – which was typically different for every location and dependent on longitude.
When well-regulated mechanical clocks became widespread in the early 19th century, each city began to use some local mean solar time.
Dowd's system was never accepted by American railroads. Allen, the editor of the Traveler's Official Railway Guide.
The borders of its time zones ran through railroad stations, often in major cities.
On November 2, 1868, the then British colony of New Zealand officially adopted a standard time to be observed throughout the colony, and was perhaps the first country to do so.