Timezones
The legal times in the various countries are based on a time scale called UTC, which many years ago replaced the well-known "Greenwich Mean Time" (GMT). By applying the appropriate time zone, if we have one instant expressed in UTC we can easily get the legal time. Often, we have to account for the Daylight Saving Time (DST) or "summer time" when applicable. For example, Great Britain uses UTC as its official time, except by summer time.
Here are a few time zones, with the difference from UTC and whether they use DST or not:
| Country | City / Area | Standard time offset | DST? |
|---|---|---|---|
| USA | Hawaii | UTC-10:00 | No |
| USA | Alaska | UTC-09:00 | Yes |
| Canada | Vancouver | UTC-08:00 | Yes |
| USA | Los Angeles | UTC-08:00 | Yes |
| USA | Boise, Denver | UTC-07:00 | Yes |
| Canada | Winnipeg | UTC-06:00 | Yes |
| USA | Chicago | UTC-06:00 | Yes |
| USA | Detroit, New York | UTC-05:00 | Yes |
| UK | London | UTC | Yes |
| Malaysia | - | UTC+08:00 | No |
| Australia | Perth | UTC+08:00 | No |
| Australia | Darwin | UTC+09:00 | No |
| Australia | Brisbane | UTC+10:00 | No |
| Australia | NSW: Canberra, Currie, Sydney | UTC+10:00 | Yes |
| New Zealand | - | UTC+12:00 | Yes |
| Kiritimati (Christmas Is.) | - | UTC+14:00 | No |
For example, if an event takes place at 5:23 UTC, then the legal time in Hawaii will be 19:23 (of previous day), while in Los Angeles will be 21:23 (or 22:23 if DST is in force), again in the previous day.
Do not be confused by the names that are sometimes given to timezones: for example, the timezone for Hawaii could be designated as "GMT+10", but you still need to subtract hours from UTC to find the legal time, and not the opposite as the misleading designation could suggest. Also note that while "GMT" has not been defined nor maintained as a standard timescale for decades, it is often used to refer to the UTC+0 timezone, although this should be avoided.
The data in the table are valid for June 2010, and please note that timezones may change over time.