[LEAPSECS] Leap second relationship to ISO 8601

[Tony Finch]

Brooks Harris <brooks at edlmax.com> wrote:
> On 2014-08-27 05:22 AM, Tony Finch wrote:
> >
> > ISO 8601 does not represent daylight saving nor time zones.
>
> It can represent both, but incompletely, or ambiguously. The "time element"
> called "zone designator" conflates "offset from UTC" and "Daylight Savings
> offset" in the "time element" called "zone designator".

The offset from UTC does not identify the time zone: many time zones can
have the same offset. The offset does not tell you whether DST is in
effect: you need to know the details of the time zone in order to work it
out.

> > > For example, a date and time in New York City might be represented
> > > as 2014-07-04T00:00:00-05:00 which misses the fact that Daylight was
> > > in effect, or 2014-07-04T00:00:00-04:00 which misses the fact the
> > > the fixed timezone offset is -05:00.
> >
> > The former is incorrect.
>
> Incorrect where?

The UTC offset in New York at that time was not -05:00 so that cannot be a
time in New York.

> Most explainations, and the spec itself, say that NTP does not account
> for Leap Seconds, and it does not, *explicitly*. Note, however, that
> 2272060800 secs / 86400 = 26297 days *exactly*. There were 10 Leap
> Seconds in effect at 1972-01-01T00:00:00Z (UTC), so there must be 10
> Leap Seconds in effect at the NTP "prime epoch of era zero", "0 h 1
> January 1900 UTC".

That reasoning is faulty. Figure 4 of RFC 5905 also says that the
NTP timestamp for 1999-12-31 is 3155587200, and
(3155587200-2272060800)/86400 is 10226 days exactly.

You cannot infer the number of leap seconds between two NTP or POSIX
time stamps, because both time scales handle leap seconds out of band.

Tony.
-- 
f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
Trafalgar: Cyclonic in northwest, otherwise mainly northerly or northwesterly
5 or 6. Slight or moderate. Showers in northwest. Good.