[net.micro.mac] Daylight Savings Time vs. Macintosh

bjf@utcs.UUCP (Bruce Freeman) (04/29/85)

Well it is that time of year again when we all get to fool around with clocks
again. In addition to the kitchen clock, the alarm clock, the VCR, the cable
converter, the ... I also have to change the clock on something that should
know better, namely my Mac. I had to do it last fall as well but with all the
talk about ROM upgrades and new system files maybe something can be done about
it. There is no reason why my Mac can't automatically fool around with its
clock to handle daylight savings time. Every UNIX system I know of can handle
DST automatically and I see no reason why any other computer OS can't. In the
system file have a resource that indicates whether DST applys. This way DST
can be customized for Europe and so on. When DST rolls around (or rolls out)
the Mac can then automatically change its clock. The algorithm is simple and
not huge. How about it Apple? 
-- 
Bruce Freeman	University of Toronto	{decvax|ihnp4|utzoo}!utcs!bjf

howard@amdahl.UUCP (Howard C. Simonson) (05/06/85)

>  ...There is no reason why my Mac can't automatically fool around with its
> clock to handle daylight savings time...
> -- 
> Bruce Freeman	University of Toronto	{decvax|ihnp4|utzoo}!utcs!bjf

Don't limit your horizons.  When I step on a plane in N.Y. and get off
at S.F., I want Mac to say, "Time to turn back the clock."  I'm sure
there is some simple hardware solution. Now there is an interesting
engineering question. :-)
---
All events portrayed are fictitious, except what he wrote and what I wrote.
-- 
Do not walk in front of me,
   I may step on your heel.                                  Howard C. Simonson
     Do not walk behind me,          ...{dragon,hplabs,ihnp4,nsc}!amdahl!howard
        I may stop abruptly.
          Just walk beside me, and be wary of sharp turns.  --  HamuS

[ Opinion? What opinion.  I think you have the wrong guy... ]

vishniac@wanginst.UUCP (Ephraim Vishniac) (05/06/85)

> In addition to the kitchen clock, the alarm clock, the VCR, the cable
> converter, the ... I also have to change the clock on something that should
> know better, namely my Mac. I had to do it last fall as well but with all the
> talk about ROM upgrades and new system files maybe something can be done about
> it.
> ...
> The algorithm is simple and not huge. How about it Apple? 

The algorithm may be simple and small, but not universal.
Many areas in the U.S. are not on standard daylight savings time (pardon
my oxymoron); some do not use daylight savings time at all.  Will you add
controls to the control panel for describing the local dst rules?  Or will
the Mac simply ask where you live?
-- 
Ephraim Vishniac
  [apollo, bbncca, cadmus, decvax, harvard, linus, masscomp]!wanginst!vishniac
  vishniac%Wang-Inst@Csnet-Relay

jer@peora.UUCP (J. Eric Roskos) (05/10/85)

>  Don't limit your horizons.  When I step on a plane in N.Y. and get off
>  at S.F., I want Mac to say, "Time to turn back the clock."  I'm sure
>  there is some simple hardware solution. Now there is an interesting
>  engineering question. :-)

Since this has a :-), I can't tell if it is a joke, or a comment on the
original suggestion.

The original suggestion actually was very reasonable.  As the author
mentioned, Unix* handles DST correctly.  Except for two years which had
anomalies, the rules for when daylight savings time starts and stops are
simple and well-defined.  The code in Unix which handles this is very
short, and equivalent code could easily be included in the Mac's OS.

*Unix is a trademark of AT&T.
-- 
Full-Name:  J. Eric Roskos
UUCP:       ..!{decvax,ucbvax,ihnp4}!vax135!petsd!peora!jer
US Mail:    MS 795; Perkin-Elmer SDC;
	    2486 Sand Lake Road, Orlando, FL 32809-7642

jdb@mordor.UUCP (John Bruner) (05/10/85)

Indiana doesn't entirely ignore daylight savings time.  A few
counties do observe it because they are economically related
to out-of-state areas (e.g. the NW counties have the same
time as Chicago).

However, I don't see why the Mac needs to know where you are.
As someone else suggested, all it needs is a flag to specify
what type of daylight savings time is to be observed (none,
US, etc.)  This scheme seems to work well in UNIX (except that
apparently BSD UNIX went to DST a week early in Europe this
year).  This flag could be kept in the parameter RAM, and the
control panel could be augmented to display/set it.
-- 
  John Bruner (S-1 Project, Lawrence Livermore National Laboratory)
  MILNET: jdb@mordor.ARPA [jdb@s1-c]	(415) 422-0758
  UUCP: ...!ucbvax!dual!mordor!jdb 	...!decvax!decwrl!mordor!jdb

fritz@utastro.UUCP (Fritz Benedict) (05/10/85)

> >  ...There is no reason why my Mac can't automatically fool around with its
> > clock to handle daylight savings time...
> > -- 
> > Bruce Freeman	University of Toronto	{decvax|ihnp4|utzoo}!utcs!bjf
> 
> Don't limit your horizons.  When I step on a plane in N.Y. and get off
> at S.F., I want Mac to say, "Time to turn back the clock."  I'm sure
> there is some simple hardware solution. Now there is an interesting
> engineering question. :-)

Our VAX and SUNs (4.2bsd) know when to change from CST to CDT. 
Anyone know how many lines of code are involved?
-- 
Fritz Benedict  (512)471-4461x448
uucp: {...noao,decvax,ut-sally}!utastro!fritz
arpa: fritz@ut-ngp
snail: Astronomy, U of Texas, Austin, TX  78712

dgary@ecsvax.UUCP (D Gary Grady) (05/11/85)

> Many areas in the U.S. are not on standard daylight savings time (pardon
> my oxymoron); some do not use daylight savings time at all.  Will you add
> controls to the control panel for describing the local dst rules?  Or will
> the Mac simply ask where you live?

To the best of my knowledge, areas in the US either use national DST
rules or they stay on standard time.  Hawaii, Arizona, Puerto Rico, the
Virgin Islands, American Samoa, and part of Indiana stay on standard
time year round.  The islands are at such low latitudes that there is
relatively little change in daylight length year round.  Indiana uses
its split-zone approach so that the whole state is effectively in one
time zone during the summer months.  Arizona uses standard time year
round just to be ornery, and if you think I'm kidding you haven't spent
much time in Arizona.

European summer time rules are far more complicated, and it annoys the
dickens out of me that this information is hard to come by for
travelers.  (I once spent four days in Scotland with my watch set an
hour off and nearly missed a flight out of Glasgow as a consequence.
The only reason I didn't is that Icelandic Airlines actually came
looking for me in the airport lounge, bless 'em!!)

It would probably be possible to handle all current rules with four
entries, each recording a date and time to change and the amount to
change by.  I think a few countries have a two-step daylight savings
time system, with a different time in effect for each of the four
seasons (spring and fall being the same).  Seems not unreasonable, and I
seem to recall at least some Unix versions use something along these
lines...
-- 
D Gary Grady
Duke U Comp Center, Durham, NC  27706
(919) 684-3695
USENET:  {seismo,decvax,ihnp4,akgua,etc.}!mcnc!ecsvax!dgary

ruffwork@orstcs.UUCP (ruffwork) (05/11/85)

[]
There is one reason for not having it do it automatically -

I believe that Indiana, and I KNOW that Arizona, dont go on to
DST.  Other countries do and don't, or do it at other times....

Perhaps if it also had geography detection hardware so it would
only perform the change if in the proper geographical areas :-)

			ruffwork
			ruffwork@orstcs.cs-net.relay
			tektronix!orstcs!ruffwork

john@hp-pcd.UUCP (john) (05/11/85)

<<<

  I grew up in Indiana and I can assure you that you do not want the try and
come up with automatic time zone changing. The best way that I have found
to handle TZ's is to run the clock at GMT and have a time zone variable
that adjusts the clock to your local time. That way you need only update the
variable when you move or change zones. If your really fancy you can handle
all 26 time zones plus the few "1/2 hour" zones that exist.


John Eaton
!hplabs!hp-pcd!john

steveg@hammer.UUCP (Steve Glaser) (05/13/85)

In article <911@peora.UUCP> jer@peora.UUCP (J. Eric Roskos) writes:
>>  Don't limit your horizons.  When I step on a plane in N.Y. and get off
>>  at S.F., I want Mac to say, "Time to turn back the clock."  I'm sure
>>  there is some simple hardware solution. Now there is an interesting
>>  engineering question. :-)
>
>Since this has a :-), I can't tell if it is a joke, or a comment on the
>original suggestion.
>
>The original suggestion actually was very reasonable.  As the author
>mentioned, Unix* handles DST correctly.  Except for two years which had
>anomalies, the rules for when daylight savings time starts and stops are
>simple and well-defined.  The code in Unix which handles this is very
>short, and equivalent code could easily be included in the Mac's OS.
>
>*Unix is a trademark of AT&T.

You're forgetting one very important point.  The Mac was intended to be
an *international machine*.  While we US Chauvinists might like it, the
fact is that the algorithm used in the US is not used everywhere.
There are places that don't use DST at all and some that use it but
have different rules.

Unix also uses GMT internally.  On the Mac, this would require
additional space in the nvram for timezone data.  Also, you would get
to solve all the things that unix punted on (saudia arabia uses solar
time, there are places with timezones that are n.5 hours off GMT
[n=integer], the translation from "minutes off GMT with dstflag" to
timezone name is not 1 to 1 outside the US, etc.)

BTW, I think the :-) refered to having the Mac automagically know that
you were in S.F.  Why the Mac would "ask" you to reset the clock I
don't know since it now has enough data to do it for you, I don't know,
but...

	Steve Glaser
	tektronix!steveg

howard@amdahl.UUCP (Howard C. Simonson) (05/13/85)

> >  Don't limit your horizons.  When I step on a plane in N.Y. and get off
> >  at S.F., I want Mac to say, "Time to turn back the clock."  I'm sure
> >  there is some simple hardware solution. Now there is an interesting
> >  engineering question. :-)
> 
> Since this has a :-), I can't tell if it is a joke, or a comment on the
> original suggestion.
> 
> The original suggestion actually was very reasonable.  As the author
> mentioned, Unix* handles DST correctly.  Except for two years which had
> anomalies, the rules for when daylight savings time starts and stops are
> simple and well-defined.  The code in Unix which handles this is very
> short, and equivalent code could easily be included in the Mac's OS.
> 
> *Unix is a trademark of AT&T.

The "joke" is: how does the Mac figure out I've flown a few thousand
miles.  It would take some sort of hardware.

Try taking a 7300 on a plane and tell me what time it is when you get
to where you're going; especially if your traveling from a DST state
to a non DST state.  I don't think Unix handles that automatically
( unless the 7300 calls the time number when you land ).
-- 
Do not walk in front of me,
   I may step on your heel.                                  Howard C. Simonson
     Do not walk behind me,          ...{dragon,hplabs,ihnp4,nsc}!amdahl!howard
        I may stop abruptly.
          Just walk beside me, and be wary of sharp turns.  --  HamuS

[ Opinion? What opinion.  I think you have the wrong guy... ]

darrelj@sdcrdcf.UUCP (Darrel VanBuer) (05/16/85)

The Xerox Ethernet protocols for "what time is it?" (both PUP and XNS)
contain the following data in the reply:
GMT number of seconds from a standard EPOCH (usually 12 midnight 1 Jan 1900).
Time zone: hours E/W of GMT + extra minutes
Start of DST (the day number in the year which is the earliest of the 7
possible days in a 365 day year on which DST starts; the right one of the
seven days is of course the Sunday).
End of DST (the day number ...)
When DST does not apply, values are ones which never occur, e.g. 0 or 366.
No doubt there is someplace in the world which can't be handled by these
rules, but they've got to be rare.  These values seldom change for a
stationary system (usually only by legislative action).
-- 
Darrel J. Van Buer, PhD
System Development Corp.
2500 Colorado Ave
Santa Monica, CA 90406
(213)820-4111 x5449
...{allegra,burdvax,cbosgd,hplabs,ihnp4,orstcs,sdcsvax,ucla-cs,akgua}
                                                            !sdcrdcf!darrelj
VANBUER@USC-ECL.ARPA

jsp@unccvax.UUCP (Joel Patterson) (05/22/85)

Why all the beef about automatic time change.  I don't know about you,
but I only have to change mine twice a year, unless I am travelling.
Such a small price to pay.  At least you didn't have to pay extra for a
card like some blue machines I can think of.

jsp