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DATETIME  November 2015

DATETIME November 2015

Subject:

Re: 1/27 conference call notes: an instant can't be on 3 different days

From:

"Denenberg, Ray" <[log in to unmask]>

Reply-To:

Discussion of the Developing Date/Time Standards <[log in to unmask]>

Date:

Mon, 23 Nov 2015 16:37:19 -0500

Content-Type:

text/plain

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Parts/Attachments

text/plain (69 lines)

Yes there is only one International Date Line, and simply by virtue of its existence, for any instant there will be two locations in different days. For example, the time zones immediately East and West of the line are always on different days. (Midnight is no exception - it always begins a day. The notion that midnight ends one day and begins the next at the same time will be debunked in the revised 8601.)   

And you're right, an instant can't occur on three days.

So disregard my suggestion that some instant might occur on three days, the argument remains the same (or even stronger), that it is difficult to justify the precision feature if the only use case is measurement of a day, when it can be off by only one day.

Ray
 
> -----Original Message-----
> From: Discussion of the Developing Date/Time Standards
> [mailto:[log in to unmask]] On Behalf Of Byrd, Donald A.
> Sent: Monday, November 23, 2015 3:36 PM
> To: [log in to unmask]
> Subject: Re: [DATETIME] 1/27 conference call notes: an instant can't be on 3
> different days
> 
> There's only one International Date Line; time zones on the earth span just
> 24 hours. So it seems to me an instant can't be on more than two different
> days, regardless of where and when it occurs. Munich's time zone is nine (I
> think) hours west of the Date Line, so an event at, say, 11:45 PM on Nov. 30
> there is on December 1 anywhere more than a few hundred kilometers (or
> some such) to its east, up to the date line. It's 15 hours from the Date Line in
> the other direction, so the earliest it can be in any time zone is 15 hours
> earlier, i.e., 8:45 AM on Nov. 30.
> 
> Furthermore, an instant also can't be on _less_ than two different days,
> regardless of where and when it occurs. Well, it could be argued that an
> instant at exactly midnight somewhere is an exception! Anyway, for practical
> purposes, every instantaneous event occurs on exactly two different days.
> 
> Am I thinking clearly?
> 
> --Don
> 
> 
> On Nov 19, 2015, at 5:13 PM, "Denenberg, Ray" <[log in to unmask]> wrote:
> 
> > So Neil Armstrong’s moon event is nominally 1969-07-20, that’s the
> “official” date that it occurred (nevermind that it was on the moon, let’s just
> say July 20 is the “real” date, for discussion sake). Some observers may have
> recorded it as July 19.   And I suppose somewhere else it was recorded as July
> 21.  Would you call this “two-day” precision?  Three-day precision?
> >
> > An event in Munich may occur close to midnight so it is the next day in
> Samoa (and the previous day somewhere else?)  But it might be November
> 30 in Munich, so it is December in Samoa, or it might be December 31 in
> Munich so it is the next year in Samoa.  So the first case is 2 (or 3) day
> precision, the second is month precision and the third year precision.  And
> maybe it occurred 2009, so there you have decade precision.
> >
> > Still, all these examples are based on cases where the estimate is no more
> than a day off.  I don’t think I can convince the ISO people based on that. Are
> there other examples?
> >
> > Ray
> >
> >> -----Original Message-----
> >> From: Discussion of the Developing Date/Time Standards
> >>
> >> [---- SNIP ----]
> 
> 
> 
> ---
> Donald Byrd
> Woodrow Wilson Indiana Teaching Fellow
> Adjunct Associate Professor of Informatics Visiting Scientist, Research
> Technologies Indiana University Bloomington

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