Mark Calabretta wrote:

>  You're still not getting the point that UTC is just a representation
>  of TAI.

   OK, let me try again.

   UTC (since 1972) is a disseminated timescale that is equal to TAI
   except for additional date and time codes transmitted with the
   signal. These codes indicate the values of TAI - DTAI for each
   full minute of TAI - DTAI.

   In a reading of UTC, (the most recent values of) these date and
   time codes can be taken as is so as to yield a reading that
   approximates UT1. The codes may also be used to derive the value of
   DTAI (from a table of leap seconds since 1972), and thus, to yield
   a reading of TAI. When a timestamp is characterised as UTC
   (rather than TAI), then the first type of reading is implied.

   In order to ensure a unique derivation of TAI from a recorded
   reading of UTC in the vicinity of a positive leap second (where
   DTAI jumps up by 1 s and the value of TAI for a given value of
   TAI - DTAI is not unique), the UTC reading that corresponds to the
   earlier TAI value shall be recorded with a second field >= 60 s,
   and the other UTC reading, with a second field < 60 s.

   Michael Deckers (still trying to understand the topology you referred to)

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