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70 • Front Panel Menu System SRG-4500 User Guide (v7.0)
A full list of countries for which DST is automatically supported is shown below.
Additional Information for the Leap Second Event (UTC)
If the menu line “Leap Second” in the UTC DateTime menu is set to User Defined, the time and date fields of this
menu can be edited. If the menu line “Leap Second” is set to Off, editing is disabled.
The menu for Leap Second Event (UTC) indicates the time and date for the next addition or subtraction of a Leap
Second. At the indicated time and date, a second will be added to or subtracted from UTC Time. See previous
paragraphs regarding editing of the available menu lines.
Leap Second Event
The Leap Second event is not regular; indeed it is usually only decided a few months in advance when a Leap
Second is to be added. For this reason it is not possible for all versions of the SRG-4500 software to have the time
and date of the next event coded into the software. Historically the Earth's spin is slowing down but some scientists
think that global warming may make the Earths spin increase. In this case, Leap Seconds would occasionally need
to be subtracted.
When a positive leap second is added at 23:59:60:00 UTC, it delays the start of the following UTC day (at
00:00:00:00 UTC) by one second, effectively delaying the UTC clock.
Announcement of Leap Seconds
The International Earth Rotation and Reference Systems Service (IERS) announces the insertion of a Leap Second
whenever the difference between UTC and UT1 approaches 0.6 s, to keep the difference between UTC and UT1
from exceeding 0.9 s. IERS publishes announcements every six months, detailing whether Leap Seconds are to
occur or not, in its “Bulletin C”. Such announcements are typically published well in advance of each possible Leap
Second date - usually in early January for June 30 and in early July for December 31. Because the Earth's rotation
Table 7.8 Countries that DST is Automatically Supported
Country Start End Action Time
Australia First Sunday in
October
First Sunday in April
the following year
02:00 local standard time
(AEST=UTC+11, ACST=UTC+10.5)
Brazil Third Sunday in
October
Third Sunday in
February the
following year
DST starts at 00:00 on the third Sunday in
October and ends at 00:00 on the third Sunday
in February - unless the latter falls during
Carnaval, in which case, the end of DST is
postponed by one week. The next six times in
which the end of DST is scheduled to be
postponed are 2012, 2015, 2023, 2026, 2034
and 2037. It is unknown whether this is 00:00
local time or local standard time, so local
standard time has been chosen.
Canada Second Sunday in
March
First Sunday in
November
Since 2007, all time changes take place at
02:00 local time
New Zealand Last Sunday in
September
First Sunday in April
the following year
02:00 local standard time (NZST=UTC+12)
USA
a
a. The Energy Policy Act of 2005 Rule.
Second Sunday in
March
First Sunday in
November
Since 2007, all time changes take place at
02:00 local time
European
Union
Last Sunday in
March
Last Sunday in
October
01:00 UTC