Daylight Saving Shift

Arved Sandstrom wrote:
> Joshua Cranmer wrote:
>> In short: March, April, September, and October are hell for scheduling
>> meetings as you try to decide who is on DST and who is not.
>
> Makes you wonder why one even needs to (I acknowledge that these days a
> person does still need to, more often than not.) After all, when a
> meeting is set up for a given date it's understood to be at a certain
> time for a certain participant in a certain location. When that
> participant says 2 PM he means 2 PM regardless, and you'd think that in
> 2009 software finally could have solved these date/time problems. After
> all, it's not like the problem is exactly an extremely difficult one,
> although it seems to have taken on that mantle. I think it's more a
> commentary on the state of programming rather than on the intrinsic
> difficulty of the problem that we still have these issues.

Yes.

But it is a problem.

I don't know what Outlook does, but it does not always work well for
a reoccurring meeting scheduled over DST changes.

Arne

Arne Vajhøj

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.

Arne

Arne Vajhøj

On Sun, 01 Nov 2009 13:26:42 GMT, Arved Sandstrom
<> wrote, quoted or indirectly quoted someone who
said :

>2009 software finally could have solved these date/time problems.

The catch is every program that deals with time needs to be aware of
the shifts. Java handles most of the problem in class libraries, but
you still have the problem of data input, given that 2009-11-01 2:01
is not a unique identifier of a time instant. Most programs just
ignore the problem or use standard time.

DST is not going away. Perhaps we could use it all year. That would
get rid of the shifts which are the major bugbear.

I see no advantage in losing an hour of evening daylight in November.

Maybe we will see DST creep till it totally takes over.

The other possibility, at least for Internet communication, email and
international meetups is to use UTC.
--
Roedy Green Canadian Mind Products
http://mindprod.com

An example (complete and annotated) is worth 1000 lines of BNF.

Roedy Green

Roedy Green wrote:
> On Sun, 01 Nov 2009 13:26:42 GMT, Arved Sandstrom
> <> wrote, quoted or indirectly quoted someone who
> said :
>> 2009 software finally could have solved these date/time problems.
>
> The catch is every program that deals with time needs to be aware of
> the shifts. Java handles most of the problem in class libraries, but
> you still have the problem of data input, given that 2009-11-01 2:01
> is not a unique identifier of a time instant.

There should be an isAmbiguous method somewhere in a class.

> Most programs just
> ignore the problem or use standard time.

I don't think so. Such a program would be rather tricky to write.

> DST is not going away. Perhaps we could use it all year. That would
> get rid of the shifts which are the major bugbear.
>
> I see no advantage in losing an hour of evening daylight in November.
>
> Maybe we will see DST creep till it totally takes over.

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.

Arne

Arne Vajhøj

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!

--
Lew

Lew

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.

--
Lew

Lew

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.

--
Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth

Joshua Cranmer

On Sun, 01 Nov 2009 22:43:44 -0500, Thomas Pornin <> wrote:

> According to Roedy Green <>:
>> I see no advantage in losing an hour of evening daylight in November.
>
> Historically it is the other way round: DST is a special time shift
> applied during summer. Thus, DST does not remove an hour of evening
> daylight in November; rather, it adds an hour of evening daylight in
> March.

Rather, it removes an hour of morning daylight in March, which doesn't get
restored until November.

--
Morris Keesan --

Morris Keesan

Morris Keesan wrote:
> On Sun, 01 Nov 2009 22:43:44 -0500, Thomas Pornin <> wrote:
>
>> According to Roedy Green <>:
>>> I see no advantage in losing an hour of evening daylight in November.
>>
>> Historically it is the other way round: DST is a special time shift
>> applied during summer. Thus, DST does not remove an hour of evening
>> daylight in November; rather, it adds an hour of evening daylight in
>> March.
>
> Rather, it removes an hour of morning daylight in March, which doesn't get
> restored until November.

It does neither for me. I just get up "later" and stay up "later" by the
clock during DST. I find the longer summer days do plenty to add both morning
and afternoon daylight during that season.

Since I'm required to get to work an hour earlier (by the sun) during DST, I
get more tardiness lectures from the bosses in the summer than the winter.

I've read that the clock changes produce increased health problems, but I have
no idea how valid that assertion is.

--
Lew

Lew

Roedy Green wrote :
> Daylight saving shift back happened 2AM this 2009-11-01.

Not in Saskatchewan it didn't

--
Wojtek

Wojtek