Daylight Saving Shift

Daylight saving shift back happened 2AM this 2009-11-01.

For tips on handling DST in Java and in the OS, see
http://mindprod.com/jgloss/dst.html

Check out the links.
--
Roedy Green Canadian Mind Products
http://mindprod.com

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

Roedy Green

On 11/01/2009 06:04 AM, Roedy Green wrote:
> Daylight saving shift back happened 2AM this 2009-11-01.

Only if you live in Canada or the US.

In Australia, the shift forward happened about 28 days ago, and it
happened in New Zealand the week before (I think).
In Europe, the shift back happened last week.
In myriads of other countries, the change happens not at all or at other
times.

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.

Also, while I do appreciate your attempts to remind us of important
yearly chronological headaches, keep in mind that approximately 95% of
the world does not live in the US or Canada and thus does not follow the
same DST rules.

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

Joshua Cranmer

Joshua Cranmer wrote:
> On 11/01/2009 06:04 AM, Roedy Green wrote:
>> Daylight saving shift back happened 2AM this 2009-11-01.
>
> Only if you live in Canada or the US.
>
> In Australia, the shift forward happened about 28 days ago, and it
> happened in New Zealand the week before (I think).
> In Europe, the shift back happened last week.
> In myriads of other countries, the change happens not at all or at other
> times.
>
> 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.
[ SNIP ]

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.

AHS

Arved Sandstrom

On 11/01/2009 08:26 AM, Arved Sandstrom wrote:
> 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.

Say a meeting (via telephone, not face-to-face) takes place at 9 AM
Pacific, 5 PM British time on a recurring basis. Is the time coordinated
to UTC (therefore doesn't change during DST, you have to account for it
manually), coordinated to the US Pacific time, or is it coordinated to
the British time? Throw in another dozen localities and suddenly
publishing the local times for every participant is a nightmare.

Plus you have the messy business of trying to remember twice a year
whether or not you have to change your clocks back an hour or forward an
hour. Spring back, fall forward or fall back, spring forward? They both
sound correct to me...


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

Joshua Cranmer

Joshua Cranmer wrote:
> On 11/01/2009 08:26 AM, Arved Sandstrom wrote:
>> 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.
>
> Say a meeting (via telephone, not face-to-face) takes place at 9 AM
> Pacific, 5 PM British time on a recurring basis. Is the time coordinated
> to UTC (therefore doesn't change during DST, you have to account for it
> manually), coordinated to the US Pacific time, or is it coordinated to
> the British time? Throw in another dozen localities and suddenly
> publishing the local times for every participant is a nightmare.

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.

I myself don't understand why this gets people so twisted. I've had to
deal with plenty of phone conferences, webexes, etc etc with
participants from the West Coast through the East Coast through the
Atlantic provinces through to Europe, and it hasn't usually caused major
problems if people do proper translations.

It doesn't have to be a nightmare - that's the whole thing. If someone
says that the proposed meeting time is 3 PM local on Oct 28th of this
year, tied to Dublin, I refuse to believe that folks in the other
timezones can't locate some decent software that tells them when that is
in their spot in their local time. The actual rules for working this
stuff out are not that complicated, although lots of software developers
certainly seem to find them so.

> Plus you have the messy business of trying to remember twice a year
> whether or not you have to change your clocks back an hour or forward an
> hour. Spring back, fall forward or fall back, spring forward? They both
> sound correct to me...

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.

AHS

Arved Sandstrom

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

Not everywhere.

--
Lew

Lew

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.

--
Lew

Lew

In article <hcjv0m$mi8$>,
Joshua Cranmer <> wrote:
>On 11/01/2009 06:04 AM, Roedy Green wrote:
>> Daylight saving shift back happened 2AM this 2009-11-01.
>
>Only if you live in Canada or the US.

And then only if you don't live in Hawaii or Arizona (unless you
live in the Navajo Nation, in which case you do). The situation
in Indiana used to be *completely* insane, but it has now been
revised to be merely annoying.

All in favor of OST (Obama Standard Time), please raise your hands.

Alan
--
Defendit numerus

Alan Morgan

1.11.2009 16:09, Joshua Cranmer kirjoitti:
> Plus you have the messy business of trying to remember twice a year
> whether or not you have to change your clocks back an hour or forward an
> hour. Spring back, fall forward or fall back, spring forward? They both
> sound correct to me...
>

Rule of thumb: always towards the nearest summer.



--
Q: Why did the germ cross the microscope?
A: To get to the other slide.

Donkey Hottie

On Sun, 01 Nov 2009 03:04:39 -0800, Roedy Green wrote:

> Daylight saving shift back happened 2AM this 2009-11-01.
>
Not anywhere I've lived, apart from a year in NYC. OTOH, I've only
resided in countries that use DST but I've never seen the point. I'd
rather keep the clocks fixed and, if anything should be changed, change
business and school, etc. hours.

The most people-friendly arrangement I've met was the one India used in
the late 70s: since winter days are shorter than summer days, business
hours were adjusted accordingly: IIRC winter opening times were about two
hours less than summer hours.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Martin Gregorie