Daylight Saving Shift

Roedy Green wrote :
> The other possibility, at least for Internet communication, email and
> international meetups is to use UTC.

And database dates.

--
Wojtek

Wojtek

Arved Sandstrom wrote:
> My point was, you can always pin a meeting time to a datetime in *one*
> given location. Phrasing it as a 9 AM Pacific *and* 5 PM British is
> already a cause of problems - just phrase it as 5 PM British *or* 9 AM
> Pacific, and let the other parties worry about the translation.

Which places the onus on them to figure out that DST has arrived in a remote
country. Not a recipe for success.

Mike Schilling

Mike Schilling wrote:
> Arved Sandstrom wrote:
>> My point was, you can always pin a meeting time to a datetime in *one*
>> given location. Phrasing it as a 9 AM Pacific *and* 5 PM British is
>> already a cause of problems - just phrase it as 5 PM British *or* 9 AM
>> Pacific, and let the other parties worry about the translation.
>
> Which places the onus on them to figure out that DST has arrived in a remote
> country. Not a recipe for success.

Not on _them_, leastways not if you mean human beings. That's the whole
point of software, to take care of tasks like this. Date and time math,
especially if we stick just to the Gregorian calendar, is not exactly
that mysterious, even with DST thrown in. The information is available -
it's not hidden away. If I'm in Nova Scotia and it's August 2009, and
someone in Brussels suggests a meeting at 3 PM their time on Oct 30th of
this year, it actually only takes me less than a minute to *Google* up a
website that tells me that I'll still be in DST and they won't be...I
figure a simple app that talks to a simple database should answer a
question like that in not much more time than it takes me to call it up
and dial in the info.

Because some changes are announced pretty close to the actual switch
it's probably most convenient to look up this kind of information from a
service.

AHS

Arved Sandstrom

Lew wrote:
> Arne Vajhøj wrote:
>> Lew wrote:
>>> Arved Sandstrom wrote:
>>>> Just as for the rules for magnetic declination, I don't even try to
>>>> remember any of that. It's easy enough to work out from first
>>>> principles and local knowledge. For example, if you know that DST is
>>>> intended to give you more hours of light in the evening, that
>>>> immediately tells you in what direction the clock must go.
>>>
>>> The irony is that Daylight Savings does not give you more hours of
>>> light in the evening. It just makes people go to (and thus leave)
>>> work an hour earlier. The evening itself still has the same number
>>> of hours of light.
>>
>> Not if the evening starts when you are home from work.
>
> Then when the evening starts depends on what job you do. A farmer's
> evening starts at full dark by that definition.
>
> Doesn't it make more sense to define evening in terms of where the sun
> is than what one's profession is?
>
> I define evening as when the sun is close to setting, i.e., when the
> light begins to fade. It's a fuzzy concept, of course, but utterly not
> dependent on what the clock says.
>
> I define afternoon as when sun passes its zenith.
>
> I find other definitions stupid, as indeed I find the whole concept of
> Daylight Savings Time. Ptui! I spit on the practice!

Most people follow the clock not the sun.

Arne

Arne Vajhøj

Lew wrote:
> Roedy Green wrote:
>>> Maybe we will see DST creep till it totally takes over.
>
> Arne Vajhøj wrote:
>> The politicians make that decision.
>>
>> We just need to write the software to match those decisions.
>>
>> Note that even if DST changes were completely removed, then we
>> would still need to support it due to historical data.
>
> I would favor abolishing DST altogether. If that means leaving the
> clock set ahead of historic Standard Time settings, so be it, although
> the last time that was tried in the U.S. (in the 1970s) it was a
> failure. People objected to the children having to wait for morning
> school buses in the dark, among other things.
>
> The subject is politically controversial. Some claim energy savings due
> to the use of DST. AFAIK there's no hard evidence to support this, at
> least, not that takes into account the increase in costs due to air
> conditioning and morning lighting. Certainly there are lots of claims
> that DST saves energy, but for some reason no one ever seems to cite
> studies or methodologies to support those claims. There is a vocal but
> politically disadvantaged contingent that denies the validity of those
> claims.
>
> But our infinitely wise and benevolent governments say that it must be
> so, though somehow jurisdictions that don't use DST don't seem to suffer
> unduly thereby. As Arne points out, dates are a matter of
> socio-political mandate and our software simply must reflect the reality.

There are plenty of research in this area.

References can be found in:
http://en.wikipedia.org/wiki/DST#Energy_use
http://en.wikipedia.org/wiki/DST#Economic_effects

Arne

Arne Vajhøj

Joshua Cranmer wrote:
> On 11/01/2009 10:28 PM, Lew wrote:
>> The subject is politically controversial. Some claim energy savings due
>> to the use of DST. AFAIK there's no hard evidence to support this, at
>> least, not that takes into account the increase in costs due to air
>> conditioning and morning lighting. Certainly there are lots of claims
>> that DST saves energy, but for some reason no one ever seems to cite
>> studies or methodologies to support those claims. There is a vocal but
>> politically disadvantaged contingent that denies the validity of those
>> claims.
>
> The recent research summaries I've seen all seem to indicate that the
> impact of DST on energy use is somewhere around ±0.2% (it's a number
> that's rarely put into full context, so I'm not exactly sure what the
> percentage is of--probably average daily summer energy usage). The sign
> is naturally hotly debated in political circles whenever tweaking DST is
> bandied about.
>
> *Performs some searching to find research papers*
>
> The literature review I just finished reading seems to suggest that most
> of the conclusions about the energy-saving nature of DST were formulated
> about 25 years ago, when lighting in particular was much less efficient
> than now (the hypothetical best-case scenario for energy savings would
> be equivalent to replacing about 15% of your incandescent light bulbs
> with compact fluorescents) and also fails to take into account the
> modern shifts in habits. Its primary conclusion was "the stuff out there
> sucks, we need modern comprehensive research on this topic."
>
> Other papers recently published seem to suggest that DST may no longer
> be saving energy. That may just be a manifestation of confirmation or
> perhaps publication bias--I'd expect that people finding energy savings
> due to DST would be less likely to publish their results nowadays. I'm
> also not a big fan of DST myself.
>
> Oh well, if humanity ever discovers interplanetary or even interstellar
> travel (as well as sufficiently speedy communication to make
> chronological synchronization across disparate settlements necessary),
> the mess resulting from DST will be the least of our worries.

Wikipedia has lots of references including newer material.

Arne

Arne Vajhøj

Arved Sandstrom wrote:
> Mike Schilling wrote:
>> Arved Sandstrom wrote:
>>> My point was, you can always pin a meeting time to a datetime in
>>> *one* given location. Phrasing it as a 9 AM Pacific *and* 5 PM
>>> British is already a cause of problems - just phrase it as 5 PM
>>> British *or* 9 AM Pacific, and let the other parties worry about
>>> the translation.
>>
>> Which places the onus on them to figure out that DST has arrived in
>> a remote country. Not a recipe for success.
>
> Not on _them_, leastways not if you mean human beings. That's the
> whole point of software, to take care of tasks like this. Date and
> time math, especially if we stick just to the Gregorian calendar, is
> not exactly that mysterious, even with DST thrown in. The
> information
> is available - it's not hidden away. If I'm in Nova Scotia and it's
> August 2009, and someone in Brussels suggests a meeting at 3 PM
> their
> time on Oct 30th of this year, it actually only takes me less than a
> minute to *Google* up a website that tells me that I'll still be in
> DST and they won't be...I figure a simple app that talks to a simple
> database should answer a question like that in not much more time
> than it takes me to call it up and dial in the info.

But if it's a standing 9:00 AM meeting that moves to 8:00 AM for just
a week or two [1], the attendees have to know to check. They
generally won't. (Yes, calendar software should let you set a
meeting to a different Timezone/locale and warn you when repeated
meetings change in local time. Absolutely. it should. I don't know
of any that does.)

1. Real-life example.

Mike Schilling

Arne Vajhøj wrote:
>
> I don't know what Outlook does, but it does not always work well

Very true.

> for a reoccurring meeting scheduled over DST changes.

Arne, there was some uneeded text at the end of your post.

Mike Schilling

Arne Vajhøj wrote:
> Lew wrote:
>> Arne Vajhøj wrote:
>>> Lew wrote:
>>>> Arved Sandstrom wrote:
>>>>> Just as for the rules for magnetic declination, I don't even try to
>>>>> remember any of that. It's easy enough to work out from first
>>>>> principles and local knowledge. For example, if you know that DST
>>>>> is intended to give you more hours of light in the evening, that
>>>>> immediately tells you in what direction the clock must go.
>>>>
>>>> The irony is that Daylight Savings does not give you more hours of
>>>> light in the evening. It just makes people go to (and thus leave)
>>>> work an hour earlier. The evening itself still has the same number
>>>> of hours of light.
>>>
>>> Not if the evening starts when you are home from work.
>>
>> Then when the evening starts depends on what job you do. A farmer's
>> evening starts at full dark by that definition.
>>
>> Doesn't it make more sense to define evening in terms of where the sun
>> is than what one's profession is?
>>
>> I define evening as when the sun is close to setting, i.e., when the
>> light begins to fade. It's a fuzzy concept, of course, but utterly
>> not dependent on what the clock says.
>>
>> I define afternoon as when sun passes its zenith.
>>
>> I find other definitions stupid, as indeed I find the whole concept of
>> Daylight Savings Time. Ptui! I spit on the practice!
>
> Most people follow the clock not the sun.
>
> Arne

Indeed. When I got on the bus after work yesterday (Monday), it was
pitch dark, yet I was able to correctly wish the bus driver Good Afternoon.

AHS

Arved Sandstrom

In comp.lang.java.programmer message <hcnnf9$gsq$-
september.org>, Mon, 2 Nov 2009 14:45:58, Mike Schilling
<> posted:
>Arved Sandstrom wrote:
>> My point was, you can always pin a meeting time to a datetime in *one*
>> given location. Phrasing it as a 9 AM Pacific *and* 5 PM British is
>> already a cause of problems - just phrase it as 5 PM British *or* 9 AM
>> Pacific, and let the other parties worry about the translation.
>
>Which places the onus on them to figure out that DST has arrived in a remote
>country. Not a recipe for success.

Clearly the Southern Hemisphere will never put its clocks forward and
back on the same days as the Northern; and, as it seems to be generally
agreed that Summer Time should be longer than Winter Time (starting near
the Spring Equinox but finishing over a month later than the Autumn
one), they'll not change in the opposite direction on the same dates
either. There is therefore an essential disagreement between those who
have Summer Time in July, those who do not have it, and those who have
it in January; and the Lines of Disagreement follow, very approximately,
the Tropics of Capricorn and Cancer, with some regions being anomalous.

In the Northern Hemisphere, the vast majority of places which change
their clocks have chosen to do so on the last Sundays of March and
October : In Europe, all but the Far East do it at 01:00 UTC, and in
Asia all outside the Middle East change on the same dates but at a fixed
local time.

The only[1] Northern country which has chosen to act otherwise and use
different dates is the USA.

The problem that you[2] see is therefore of your own creation, and
sympathy from outside should not be expected. You, through your
"democratic" system, should have chosen to move to use the same dates as
the vast majority of Northern Hemisphere clock-changing countries with a
substantial majority of Northern Hemisphere clock-changing people. Then
you would only have date difficulty when dealing with the Deep South.


[1] Canada made no choice; there, the matter is left to the Provinces.
The Provinces all made the same choice of date, but they did not make it
simultaneously. Mexican rules also depend on location. The rest of
clock-changing North America is in practice a minor detail.

[2] Those who do not choose to indicate location or nationality are
deemed to be American.

--
(c) John Stockton, nr London, UK. ?@merlyn.demon.co.uk Turnpike v6.05.
Web <URL:http://www.merlyn.demon.co.uk/> - w. FAQish topics, links, acronyms
PAS EXE etc : <URL:http://www.merlyn.demon.co.uk/programs/> - see 00index.htm
Dates - miscdate.htm estrdate.htm js-dates.htm pas-time.htm critdate.htm etc.

Dr J R Stockton