zoneinfo-right; leap seconds

Markus Kuhn Markus.Kuhn at
Wed May 27 12:00:49 UTC 1998

"Joseph S. Myers" wrote on 1998-05-26 17:01 UTC:
> On Tue, 26 May 1998, Olson, Arthur David wrote:
> > On leap seconds: having a single leap second file would eliminate the
> > ability to have "rolling" leap seconds. (This was provided when, one
> > year, the city of New York announced that the countdown for the dropping
> > of the big ball that marks the beginning of the new year would run
> > "3...2...1...LEAP...Happy New Year!", putting the leap second at
> > midnight local time. The time zone data as distributed reflects
> > internationally agreed
> > leap-second-occurs-at-the-same-instant-everywhere-on-Earth behavior.)
> Has anywhere (with a UTC-based time zone) ever _legally_ instituted such a 
> move of a leap second?

There never was such a thing as a rolling leap second. If the city of New York
really started to publish their own time scale with a leap second at
04:60Z = 23:60-05, then they would be running 1 s ahead of US/CA Eastern
Time from 19:00 to 23:60 of their NY time. This New York counting sounds
very much like an intellectual accident of someone who has heard about
leap seconds but didn't understand them fully.

As far as I know, there is no geographic region that uses an official
time scale with leap seconds but is at the same time not defined by one
(or two if summer time is used) fixed offsets to UTC. In the GPS age,
there is really no point in having non-UTC-based civil time zones.


Markus G. Kuhn, Security Group, Computer Lab, Cambridge University, UK
email: mkuhn at,  home page: <>

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