[tz] Looking for details on timezones “right/…”

[Paul Gilmartin]

On 1/17/23 11:57:53, Robert Elz via tz wrote:

>      Date:        Sun, 15 Jan 2023 18:40:27 +0100
>      From:        =?utf-8?Q?Jens_Tr=C3=B6ger?= via tz <tz at iana.org>
>      Message-ID:  <2FB37B4F-3F85-4260-8C49-D770591075C6 at light-speed.de>
> 
>    | Today I stumbled upon timezone strings like “right/UTC”,
> 
> Many systems don't bother installing those, as they're not usually
> very useful on POSIX systems.
> 
>    | I’m unable to find details on the meaning & classification of the
>    | “right/” here and how it relates to actual UTC and other timezones.
> 
> The right/* zones convert genuine UTC (that is, the time that occasionally
> steps 23:59:58 23:59:59 23:59:60 00:00:00 00:00:01) with leap seconds
> counted.

My experiments appear to show that TZ=right/* results in computing the time
for zone "*" as if time() returned TAI-10 seconds.  This is the current
IBM recommended setting of hardware clocks on IBM mainframes, which ran on
GMT until the inception of UTC in 1972 when TAI was 10 seconds ahead of UTC.
IBM switched to running clocks at the atomic rate and introduced the
10-second offset in order to avoid a discontinuity.

UTC is currently 37 (leap) seconds behind TAI.
     529 $ uname -a
     Linux debian 4.19.0-23-amd64 #1 SMP Debian 4.19.269-1 (2022-12-20) x86_64 GNU/Linux
     530 $ TZ=right/Universal date; TZ=Universal date
     Wed 18 Jan 2023 12:23:07 AM UTC
     Wed 18 Jan 2023 12:23:34 AM UTC
     531 $

I have not experimented with TZ=right/* for dates prior to 1972.
     <http://leapsecond.com/java/gpsclock.htm>

-- 
gil