[LEAPSECS] An example

Warner Losh imp at bsdimp.com
Tue Nov 2 17:03:49 EDT 2010

On 11/02/2010 14:38, Poul-Henning Kamp wrote:

> In message<20101102202753.GC21438 at ucolick.org>, Steve Allen writes:

>> On Tue 2010-11-02T20:22:29 +0000, Poul-Henning Kamp hath writ:

>>> It admits no such thing, and for all I know, and despite your

>>> complaints about the lack of an "essen" unit, that there is more

>>> than one definition of a second in use at present ?

>> Section A.4.15

>> http://www.opengroup.org/onlinepubs/9699919799/xrat/V4_xbd_chap04.html


>> "Note that as a practical consequence of this, the length of a

>> second as measured by some external standard is not specified."


>> Is this not the POSIX standard?

> Technically it is not, it is the Open Group standard, but that's not

> material.


> There is a difference between "not specified" and "different from".


> I know of no compliant system, where seconds are not SI-second length

> to the best of the ability of the hardware and software.


> If you want to carry this point, please quote actual system documentation

> that specifies a goal of having seconds different from SI seconds.

Especially in light of:

"the value is related to a Coordinated Universal Time name ..."

which explicitly invokes UTC, which ticks explicitly in SI seconds.

Those statements, imho, are there to decline to set a maximum error
between the time the system thinks it is, and the time that NIST or some
other national body thinks it is. A standards compliant system could be
345 seconds different than the time NIST publishes via their NTP
servers. A standards compliant system could also be off by 12us. The
application programmer has no way of knowing that error and shouldn't
rely on it being smaller than any specific amount.


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