- If each town were to keep the time of its meridian, there would be much difference in local time between one town and the other.
- Travellers going from one end of the country to the other would have to keep changing their watches if they wanted to keep their appointments. This is impractical and very inconvenient.
- To avoid all these difficulties, a system of standard time is observed by all countries.
- Most countries adopt their standard time from the central meridian of their countries.
- In larger countries such as Canada, the U.S.A., China, and the U.S.S.R., it would be inconvenient to have a single time zone. So these countries have multiple time zones.
- Both Canada and the U.S.A. have five time zones—the Atlantic, Eastern, Central, Mountain, and Pacific Time Zones. The difference between the local time of the Atlantic and Pacific coasts is nearly five hours.
- Russia has nine time zones.