[LEAPSECS] Footnote about CCITT and UTC

[Tony Finch]

On Sun, 14 Dec 2008, Zefram wrote:

>

> 	NOTE  These expressions apply to both UTC and non-UTC based time

> 	scales for time of day.

>

> This seems to be the crucial bit that you missed.  It's explicit about

> allowing time scales other than UTC, and doesn't restrict the choice

> of time scale at all.  UT1, with strict 86400-second days, is obviously

> permitted, and I suggest that vague UT per se is also a valid time scale.


Ah, yes, thanks for pointing that out, and also


> 	*local time*

>

> 	locally applicable time of day such as standard time of day,

> 	or a non-UTC based time of day

>

> You're permitted to represent, for example, the mean-solar-time-based

> British legal time in ISO 8601.


However...


> Unfortunately ISO 8601 does not supply any way to designate UT1 or any

> other flavour of UT except UTC.  Thus, strictly speaking, there is no

> way to designate any local time that is based on UT1 rather than UTC.


So non-UTC time has only minimal support by the standard.


> It seems to me that the standard would be rather more useful if "standard

> time" were defined more according to its original meaning: a local time

> scale defined by an offset from UT, rather than specifically from UTC.

> The timezone designation material should correspondingly refer to UT

> rather than UTC, and the "Z" should probably follow by designating UT.

> All of these would be explicitly vague as to which flavour of UT is

> being referred to.


Yes, I think this kind of vagueness makes sense in a lot of situations
(with appropriate caveats for applications that require subsecond
precision and agreement between multiple systems). It would work for POSIX
time too.

Tony.
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