User Guide

Advanced Topics
123
What are time zones?
People expect that the time reflects the sunset. Dawn should be in the morning maybe around 06:00
and dusk in the evening maybe at 20:00. These times will obviously vary depending on the season.
It would be very confusing if everyone on earth would use the same global time as this would
correspond to the sunset only at a small part of the world.
For that reason, the earth is split into several different time zones, each zone with a local time that
corresponds to the local sunset.
The time zone's base time is UTC (Coordinated Universal Time) or Zulu Time (military and
aviation). The older term GMT (Greenwich Mean Time) shouldn't be used as it is slightly incorrect
(up to 0.9 seconds difference to UTC). The UTC base time equals to 0 (based at Greenwich, England)
and all time zones have an offset to UTC between -12 to +14 hours!
For example: If you live in Berlin you are in a time zone one hour earlier than UTC, so you are in
time zone "+1" (time difference in hours compared to UTC). If it's 3 o'clock in Berlin it's 2 o'clock
in UTC "at the same moment".
Be aware that at a few places on earth don't use time zones with even hour offsets (e.g. New Delhi
uses UTC+05:30)!
Further information can be found at: http://en.wikipedia.org/wiki/Time_zone and http://
en.wikipedia.org/wiki/Coordinated_Universal_Time.
What is daylight saving time (DST)?
Daylight Saving Time (DST), also known as Summer Time, is intended to "save" some daylight
during the summer months. To do this, a lot of countries (but not all!) add a DST hour to the already
existing UTC offset. So you may need to take another hour (or in very rare cases even two hours!)
difference into your "time zone calculations".
Unfortunately, the date at which DST actually takes effect is different throughout the world. You
may also note, that the northern and southern hemispheres have opposite DST's (e.g. while it's
summer in Europe it's winter in Australia).
Keep in mind: UTC remains the same all year around, regardless of DST!
Further information can be found at: http://en.wikipedia.org/wiki/Daylight_saving.
Further time zone and DST information can be found at: http://wwp.greenwichmeantime.com/ and http://
www.timeanddate.com/worldclock/.
7.5.1. Set your computer's time correctly!
If you work with people around the world, it's very helpful to set your computer's time and time zone right.
You should set your computers time and time zone in the correct sequence:
1. Set your time zone to your current location
2. Set your computer's clock to the local time