## 1228Re: [ISO8601] Re: meaning of time-interval

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• Feb 1, 2005
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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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