## 1233Re: meaning of time-interval

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• Feb 3, 2005
Although we now use a strict ordinal counting of the days of the
month, originally the extra day was added to the 24th day of February,
i.e. the 24th was counted as two days, followed by the 25th-28th. In
Roman backwards counting, this was the sixth day before the kalends of
March, and the extra day was called the second-sixth, or "bissextile".
Traditionally, feast days of saints in February after this day were
celebrated one day later in leap years. So you see, the last day of
February remains the last day of February even in leap years. See
http://en.wikipedia.org/wiki/Leap_year#Which_day_is_the_leap_day.3F

Of course, few now count days this way, and even the Church has
recently started following an ordinal count. And you can celebrate
your birthday any day you wish; my brother celebrates his in June,
since he was born on Christmas Eve, and that's a sucky time to
celebrate a birthday.

Besides, nobody else born the several days of February celebrates a
day later during leap years; if they were born on the 27th day of
February, on any year, they celebrate on the 27th of February on both
normal and leap years, even though its the 3rd day of kalends in
normal years and the 4th in leap years.

John Hynes

--- In ISO8601@yahoogroups.com, NGUYEN Adam <ivy19991231@s...> wrote:
> For the birthday on 29 February, I (personally) probably would
> celebrate it on 1 March on non-leap years if I had such a birthday,
because
> 28 February on any kind of year is before 29 February.
>
> Something slightly off-topic, but may apply to the latest
> discussions on here has to do with my wristwatch, a Casio G-Shock
that has
> the date in YYYY M- D ('2000 1- 13' for 13 January 2000) format
and time
> in 24-hour format. I can set any of the five alarms to go off on
certain
> dates: either every day in a particular month (shown as ' 1- - -' for
> every day in January), every month on a particular day (like every
15th day
> of every month, shown as '- --15' for the 15th day of every month),
or on
> an exact date (like every 14 January, shown as ' 1-14'). I wonder what
> would happen should I set the alarm to go off on every 31st day, or a
> similar day number within a month. Perhaps it will sound only seven
times a
> year (on the months with 31 days)? If not, I would guess the next
logical
> thing it should do would be to sound on the last day of every month.
>
> Any opinions?
>
> PS: I wonder why ISO 8601 doesn't allow for time zone offsets beyond
> minute-resolution (eg. YYYY-MM-DDTHH:mm:ss±hh:mm:ss.sss) (like that
> historical Netherlands offset having centisecond-resolution).
>
> At 2005-02-01 16:31 (UTC+0000), you wrote:
>
>
> >If someone was born on 2004-02-29 when is their first birthday? You
> >might say 2005-03-01 or 2005-02-28. Does that mean that they have the
> >same birthday as someone born on 2004-03-01 or 2004-02-28?
> >
> >There is a general expectation of addition that subtraction of the
> >addend from the sum gives the original.
> >
> >Arbitrary arithmetic is not be possible using any units. You cannot
> >add anything to 1997-06-30T23:59:60Z except for 1Y6M and similar. A
> >small number of seconds would be okay but a large interval could not
> >extend more than a few months into the future because of
> >unpredictability of leap seconds. Any other units would produce a
> >result with 60 in the seconds.
> >
> >The only way to do correct interval arithmetic is to use something
> >like TAI. But that is off topic for ISO 8601.
> >
> >IMHO the intent of time-intervals involving duration in ISO 8601 is
> >that the start + duration or end - duration should (must?) be a valid
> >date-time without having to apply any normalization rules.
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