Manual Time zone Selection 
Usually, it is not necessary and not recommended to select the time zone manually, because this computer program knows which time zones apply to which places for what times, and has complete information about daylight saving time.

In some very rare cases a user may have better information about time zones and daylight saving time than the database used here. For example, there are areas of doubt for some years in Vietnam, and for many parts of the former Soviet Union.

In such cases it may be necessary to select a manual time zone in the pull-down list. To return to automatic time zone, please select the top item in the list.