Tech Insider					     Technology and Trends


			      USENET Archives

Newsgroups: comp.realtime,sci.geo.satellite-nav,comp.programming,netcom.general
Path: nntp.gmd.de!xlink.net!howland.reston.ans.net!europa.eng.gtefsd.com!
library.ucla.edu!csulb.edu!csus.edu!netcom.com!mcmahan
From: mcma...@netcom.com (Dave Mc Mahan)
Subject: How to determine when daylight savings time switches?
Message-ID: <mcmahanCrJt3v.421@netcom.com>
Followup-To: poster
Keywords: daylight savings time
Organization:  Dave McMahan @ NetCom Services 
Date: Fri, 17 Jun 1994 15:45:30 GMT
Lines: 18

I have been asked to find out how to determine the exact date used to cause
a switch from standard time to daylight savings time.  I know that there
are two such switches each year (one in the fall to switch to standard time
and one in the spring to switch to daylight savings time) and I know that
the switch always occurs early on a Sunday morning, but I need to know how
those particular days are selected.  Can you help me?

If there are places that pick the date to switch in non-standard ways, I
would like hear about those as well.

Please send all replies directly to the poster (mcma...@netcom.com), since
this is being put into several newsgroups at once.


   -dave
-- 
Dave McMahan                            mcma...@netcom.com
                                        37N 17.382    121W 59.190 

Newsgroups: comp.realtime,sci.geo.satellite-nav,comp.programming,netcom.general
Path: bga.com!news.sprintlink.net!hookup!swrinde!news.dell.com!tadpole.com!
uunet!newsgate.watson.ibm.com!hawnews.watson.ibm.com!mojo!mouser
From: mou...@watson.ibm.com (Joe Seigh)
Subject: Re: How to determine when daylight savings time switches?
Sender: n...@hawnews.watson.ibm.com (NNTP News Poster)
Message-ID: <Crt1sv.7AsM@hawnews.watson.ibm.com>
Date: Wed, 22 Jun 1994 15:31:43 GMT
Disclaimer: This posting represents the poster's views, not necessarily those 
of IBM.
References: <2u9dei$p62@NE3995.rabo.nl>
Nntp-Posting-Host: mojo.watson.ibm.com
Organization: IBM T.J. Watson Research
Keywords: daylight savings time
Lines: 9

The heck with daylight savings time.  What I want to know is how that
leap second that they are supposed to tack on to the end of June works.  None
of the unices I've looked at seem to be able to handle it.  Basically
I think you have to decrement a second from the epoch which means a
defacto moving the definition of start of the epoch up a second.

BTW, when is the second added, local time or GMT?

Joe Seigh

Path: bga.com!news.sprintlink.net!hookup!swrinde!howland.reston.ans.net!EU.net!
sunic!trane.uninett.no!nntp.uio.no!nntp-oslo.uninett.no!naggum.no!erik
From: Erik Naggum <e...@naggum.no>
Newsgroups: comp.realtime,sci.geo.satellite-nav,comp.programming,netcom.general
Subject: Re: How to determine when daylight savings time switches?
Date: 22 Jun 1994 18:54:41 UT
Organization: Naggum Software; +47 2295 0313
Lines: 20
Message-ID: <19940622.3190@naggum.no>
References: <2u9dei$p62@NE3995.rabo.nl> <Crt1sv.7AsM@hawnews.watson.ibm.com>
NNTP-Posting-Host: naggum.no

[Joe Seigh]

|   What I want to know is how that leap second that they are supposed to
|   tack on to the end of June works.  None of the unices I've looked at
|   seem to be able to handle it.  Basically I think you have to decrement
|   a second from the epoch which means a defacto moving the definition of
|   start of the epoch up a second.

have you attempted to touch a file at 23:59:60?  will it still read 23:59:60?

|   BTW, when is the second added, local time or GMT?

Coordinated Universal Time (UTC).  GMT doesn't _have_ leap seconds.

</Erik>
--
Erik Naggum <e...@naggum.no> <S...@ifi.uio.no>       |  memento, terrigena
ISO 8652 Ada/ISO 8879 SGML/ISO 9899 C/ISO 10646 UCS  |  memento, vita brevis

ftp://ftp.ifi.uio.no/pub/SGML           wais://ftp.ifi.uio.no/comp.text.sgml

Path: bga.com!news.sprintlink.net!hookup!news.moneng.mei.com!
howland.reston.ans.net!xlink.net!fauern!rrze.uni-erlangen.de!not-for-mail
From: unr...@cd4680fs.rrze.uni-erlangen.de (Markus Kuhn)
Newsgroups: comp.realtime,sci.geo.satellite-nav,comp.programming,netcom.general
Subject: Re: How to determine when daylight savings time switches?
Date: Fri, 24 Jun 1994 13:00:51 +0200
Organization: Regionales Rechenzentrum Erlangen, Germany
Message-ID: <2ueed3E2vj@uni-erlangen.de>
References: <2u9dei$p62@NE3995.rabo.nl> <Crt1sv.7AsM@hawnews.watson.ibm.com> 
<19940622.3190@naggum.no>
Reply-To: msk...@cip.informatik.uni-erlangen.de
NNTP-Posting-Host: cd4680fs.rrze.uni-erlangen.de
Lines: 53

Erik Naggum <e...@naggum.no> writes:

>GMT doesn't _have_ leap seconds.

Wrong.

GMT is London winter time, and it is defined to be identical to UTC, so of
course if UTC jumps, so does GMT. Perhaps you mean that "mean solar time" and
UT0 don't have leap seconds? Yes, that's right. Without huge comet impacts,
the earth won't jump a second.

Recommended reading: IERS (International Earth Rotation Service) Bulletins
and RFC 1305. There you'll also find references to non-ftpable literature.
(e.g. ftp.uni-erlangen.de:pub/IERS/).

E.g. from RFC 1305 a very brief introduction to time:

------------------------------------------------------------------------
Determination of Time and Leap Seconds

The International Bureau of Weights and Measures (IBWM) uses
astronomical observations provided by the U.S. Naval Observatory and
other observatories to determine UTC. Starting from apparent mean solar
time as observed, the UT0 timescale is determined using corrections for
Earth orbit and inclination (the Equation of Time, as used by sundials),
the UT1 (navigator's) timescale by adding corrections for polar
migration and the UT2 timescale by adding corrections for known
periodicity variations. While standard frequencies are based on TAI,
conventional civil time is based on UT1, which is presently slowing
relative to TAI by a fraction of a second per year. When the magnitude
of correction approaches 0.7 second, a leap second is inserted or
deleted in the TAI timescale on the last day of June or December.

For the most precise coordination and timestamping of events since 1972,
it is necessary to know when leap seconds are implemented in UTC and how
the seconds are numbered. As specified in CCIR Report 517, which is
reproduced in [BLA74], a leap second is inserted following second
23:59:59 on the last day of June or December and becomes second 23:59:60
of that day. A leap second would be deleted by omitting second 23:59:59
on one of these days, although this has never happened. Leap seconds
were inserted prior to 1 January 1991 on the occasions listed in Table
8 (courtesy U.S. Naval Observatory). Published IBWM corrections
consist not only of leap seconds, which result in step discontinuities
relative to TAI, but 100-ms UT1 adjustments called DUT1, which provide
increased accuracy for navigation and space science.
------------------------------------------------------------------------

Markus

-- 
Markus Kuhn, Computer Science student -- University of Erlangen,
Internet Mail: <msk...@cip.informatik.uni-erlangen.de> - Germany
WWW Home: <http://wwwcip.informatik.uni-erlangen.de/user/mskuhn>

Newsgroups: comp.realtime,sci.geo.satellite-nav,comp.programming,netcom.general
Path: bga.com!news.sprintlink.net!hookup!usc!elroy.jpl.nasa.gov!ucla-cs!twinsun!
eggert
From: egg...@twinsun.com (Paul Eggert)
Subject: Re: How to determine when daylight savings time switches?
Message-ID: <CrxI9J.AyH@twinsun.com>
Sender: use...@twinsun.com
Nntp-Posting-Host: tattoo
Organization: Twin Sun Inc, El Segundo, CA, USA
References: <2u9dei$p62@NE3995.rabo.nl> <Crt1sv.7AsM@hawnews.watson.ibm.com> 
<19940622.3190@naggum.no> <2ueed3E2vj@uni-erlangen.de>
Date: Sat, 25 Jun 1994 01:17:42 GMT
Lines: 17

unr...@cd4680fs.rrze.uni-erlangen.de (Markus Kuhn) writes:

> Erik Naggum <e...@naggum.no> writes:
> > GMT doesn't _have_ leap seconds.

> Wrong.  GMT is London winter time,

You're both right.  The problem is that there are two disagreeing
interpretations of the term ``GMT'': the official definition ``mean
solar time observed at Greenwich'' used by Naggum, and the unofficial
meaning ``time used by the BBC World Service'' used by Kuhn.
Since nobody has really used the official definition of GMT for decades,
pedantic timekeepers avoid saying ``GMT'' these days;
it avoids confusion and prevents arguments.

By the way, ``London winter time'' was UT+0100 from 1940 through 1945,
and from 1968 through 1971, so in that sense, at least, Kuhn is incorrect.

			        About USENET

USENET (Users’ Network) was a bulletin board shared among many computer
systems around the world. USENET was a logical network, sitting on top
of several physical networks, among them UUCP, BLICN, BERKNET, X.25, and
the ARPANET. Sites on USENET included many universities, private companies
and research organizations. See USENET Archives.

		       SCO Files Lawsuit Against IBM

March 7, 2003 - The SCO Group filed legal action against IBM in the State 
Court of Utah for trade secrets misappropriation, tortious interference, 
unfair competition and breach of contract. The complaint alleges that IBM 
made concentrated efforts to improperly destroy the economic value of 
UNIX, particularly UNIX on Intel, to benefit IBM's Linux services 
business. See SCO vs IBM.

The materials and information included in this website may only be used
for purposes such as criticism, review, private study, scholarship, or
research.

Electronic mail:			       WorldWideWeb:
   tech-insider@outlook.com			  http://tech-insider.org/