[ntp:questions] Leap second to be introduced in June

Terje Mathisen terje.mathisen at tmsw.no
Fri Jan 16 07:07:07 UTC 2015

cmadams at cmadams.net (Chris Adams) wrote:
> Once upon a time, Phil W Lee  <phil at lee-family.me.uk> said:
>> For the tiny number of programs which really need UTC (not TAI), it
>> would just be a different number, but the only thing I know of which
>> really needs UTC rather than TAI would be programs to assist with
>> astronomy or astral navigation.
> I think one problem with OS clocks in TAI is that counting it correctly
> requires active/on-going maintenance at unknownable intervals for all
> systems that use any form of timestamps (including for example anything
> that uses network file systems).
> Also, you can't properly represent future timestamps (necessary for some
> things) as seconds since an epoch, and that's pretty widely used.  By
> that I mean that the number of seconds between 2015-06-30 23:59:00 and
> 2015-07-01 00:00:00 has changed since last month.
Adn this is _exactly_ why it is always a bad idea to use (UTC) seconds 
for those future timestamps:

If you actually mean that something has to happen N seconds from now, 
that future timestamp has to be in TAI, since using UTC would obviously 
blow up across any leap second, right?

If you instead meant a calendar event, then you need a different 
timescale which is either Julian Day Number (JDN) or YMD, followed by 
either HMS or an offset into the day, followed by the applicable time zone.


- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

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