On Thu 2006/01/12 02:36:44 CDT, John Cowan wrote
in a message to: LEAPSECS@ROM.USNO.NAVY.MIL

>We already have that repeated time sequence and gap in much of the world,
>and live with it.  These repetitions would be no better and no worse;
>when a gap is present, the local sovereignty can omit the gap, but this
>is not a necessary feature of the proposal.

At the start of daylight saving where I live the clocks are set forward
from 2am to 3am.  Naively it looks like there is a gap.  Likewise at the
end of daylight saving the hour from 2am to 3am appears to be repeated.

The apparent gaps and repeats are simply an artifact of what happens to
a clock display when you change it to read a different timescale.

        Standard time                 Summer time            Legal time
  ------------------------      ------------------------     ----------
  2005/10/30 00:01:58 AEST     (            :           )        :
  2005/10/30 00:01:59 AEST     (2005/10/30 00:02:59 AEDT)       AEST
  2005/10/30 00:02:00 AEST  ->  2005/10/30 00:03:00 AEDT      AEST/AEDT
 (2005/10/30 00:02:01 AEST)     2005/10/30 00:03:01 AEDT        AEDT
 (            :           )     2005/10/30 00:03:02 AEDT        AEDT
 (            :           )                 :                    :
 (            :           )                 :                    :
 (            :           )     2006/04/02 00:02:58 AEDT        AEDT
 (2006/04/02 00:01:59 AEST)     2006/04/02 00:02:59 AEDT        AEDT
  2006/04/02 00:02:00 AEST  <-  2006/04/02 00:03:00 AEDT      AEST/AEDT
  2006/04/02 00:02:01 AEST     (2006/04/02 00:03:01 AEDT)       AEST
  2006/04/02 00:02:02 AEST     (            :           )        :
              :                (            :           )        :

It should be clear that the gaps and repeats are fictitious, especially
if you think of AEST and AEDT as existing beyond the times when they are
in legal use.  Putting it in practical terms, suppose I have a traffic
accident at 0230 on 2006/04/02, what time will the police officer write
in his report?  For most times of the year he can omit the timezone spec
because there is no legal ambiguity, but to do so for this specific hour
would be insufficient, he must specify AEDT or AEST.

The situation with the proposed leap hour is quite different.  Given
that AEST is defined as UTC+1000, and AEDT as UTC+1100, would someone
care to speculate, in terms similar to the above, what will happen when
a leap hour is inserted?

Mark Calabretta
ATNF

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