[LEAPSECS] ISO 8601 Z designator improper before 1972?

M. Warner Losh imp at bsdimp.com
Mon Feb 9 13:26:10 EST 2009

In message: <09364CFCA84C4DBE82562A5A33318D50 at grendel>
"Gerard Ashton" <ashtongj at comcast.net> writes:

: Given that UTC did not exist in its present form (and as described

: in ISO 8601:2004, that is, with leap seconds) until 1 January 1972,


: and


: given that the ISO 8601:2004 standard states "[Z] is used as UTC

: designator."

: (p. 12)


: is it fair to conclude that it is improper to use the "Z" designator for any

: date/time in the ISO 8601 format prior to 1 January 1972?

Why would it be improper? UTC has existed as a continuous[*] time scale
since 1958, although the name is much newer than that. Just because
the leap second rules were different prior to 1972 doesn't mean that
UTC didn't exist prior to that. Just that the rules were different.

: If indeed that is improper, would it not be incumbent on anyone who wishes

: to express a UT time/date in a format that looks like ISO 8601 format to

: either


: (1) leave off the designator, and communicate the fact that the it is UT

: through

: some other means, or,


: (2) establish their own standard that expressly modifies ISO 8601 to

: indicate

: that "Z" is the UTC designator after 1 January 1972, and the UT designatior

: before

: then?

Usually people just assume that times before 1972 just don't have leap
seconds, but are otherwise UTC. The adjustments to UTC prior to 1972
were such that they can be viewed as continuous and the details can be
safely ignored for all but the most demanding timing applications
dealing with historical data.

Of course, you'd have to ask the ISO 8601:2004 authors if it is
improper or not.


[*] continuous means here uninterrupted, as opposed to the usual
arguments that come up at leap second over whether they are
discontinuities or just an irregular radix.

: Gerry Ashton


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