Daylight Saving Time (DST) extends beyond the astronomical summer.
Wherever it is used, it adds another time zone, defined as an area (country or region) where the same time is observed.
DST has made the original time zone structure much more complicated. Countries or regions that observe DST change time zones twice a year.
Time zone designations are both civilian and military. The list of civilian time zones includes Daylight Saving. Military time zones do not use DST.
Just like Standard Time Zones, Daylight Saving Time (DST) ones are indexed by the zone hour value, the offset or time difference relative to GMT or its successor, UTC (Universal Coordinated Time).
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