[LEAPSECS] article for Metrologia

[jimlux]

On 10/28/22 11:10 AM, Steffen Nurpmeso wrote:
> Steve Allen wrote in
>   <20221028045813.GA20487 at ucolick.org>:
>   |On Thu 2022-10-27T19:25:01-0700 Steve Allen hath writ:
>   |> Levine, Tavella, and Milton have an upcoming article for Metrologia
>   |> on the issue of leap seconds in UTC
>   |>
>   |> https://iopscience.iop.org/article/10.1088/1681-7575/ac9da5b
>   |
>   |sorry, stray character appended to my cut and paste
>   |
>   |https://iopscience.iop.org/article/10.1088/1681-7575/ac9da5
> 
> That "increasing number of applications" all through the document
> makes me angry really.  I find it astonishing to read that there
> are digital clocks that cannot display a second 60 and all that.

The digital clock by my bedside, and a variety or other clocks that 
don't have computers in them don't display second 60, nor do they handle 
going from 58 to 00.

The clocks in my various and sundry appliances also do not do this.

One can argue, who cares - whether the oven turns on a second early or 
late probably isn't a problem.

But what about the enormous number of industrial process controllers - 
almost all of which do not deal with leap seconds.  At some point, sure, 
they'll sync, either by hand, or over the network.  And that's where it 
starts to get sticky.

Do you smear or jump? If you're running a system where seconds count - 
radar is one example.  A plane moves several hundred meters/second. If 
you're tracking and sending position reports, do you transmit times in 
UTC or TAI?

There's the possibility of cooperative traffic avoidance for cars, 
planes, and boats - The data is always late, so there's an element of 
modeling taking position and velocity at time t=x-Nseconds and 
propagating that forward to t=x.




> This is just another outcome of the trivialization and
> superficialication all around.  You need a reliable source of
> time, use TAI; or distribute the offset of UT1 and UTC
> permanently, best TAI, too.  so that changes can be detected.  NTP
> does still not do it, does it.  (It is still not using DTLS but
> something else, too.  My one cent (again).)  You know how large
> these packets are?  Now that even refrigerators and light bulbs go
> online (and letting aside the privacy issues), it is all there, at
> your fingertips.  Sorry, i do not understand.


It is precisely because there is a difference between UTC and TAI (or 
GPS) that changes, and that there is no "universal" way to handle the 
change that it is a problem.  Mission critical systems will tend to 
figure something out, but it might be different.

I worked on SCaN Testbed [1] - a system that flew on ISS for a number of 
years. This inconsistency of intepretation of time (UTC, GMT, GPST, TAI) 
led us to implement a flight rule "Turn off the power 1 hour before the 
leap second and turn it on 1 hour after".  That was easier than trying 
to get everyone on the same page (everyone is a remarkably large crowd - 
experiment PIs, test controllers and engineers, payload operators, ISS 
controllers, ISS internal data bus time distribution (Broadcast 
Ancillary Data on MIL-STD-1553), not to mention the entire pipeline of 
data links up to and back down all the way to the ops center.

[1]R. C. Reinhart, T. J. Kacpura, S. K. Johnson and J. P. Lux, "NASA's 
space communications and navigation test bed aboard the international 
space station," in IEEE Aerospace and Electronic Systems Magazine, vol. 
28, no. 4, pp. 4-15, April 2013, doi: 10.1109/MAES.2013.6506824.

> 
> And _i_ do not want to hear "o-ho-ho, but there is a difference in
> between solar time and the time zone anyhow", there is
> a difference also in between a priest and a wise man, and you
> better conform to the former or they kill you.  Really.
> (I would never let temples be driven by engineers, not even if
> they are permanently joined by their wifes.)
> 
> To me it remains a cultural achievement that we can track the
> offset so exactly, and this cultural achievement is practically
> shared by a lot of human cultures (if you want to grant these
> beasts such, especially the west, goodness, gracious, great balls
> of fire!), as many of them have a relation to the sun (the big LED
> / infrared thing on the blue screen, you know).
> 
> Distribution of leap seconds into time and date applications is
> a problem.  Clock calculations with UNIX epoch are all wrong given
> the current semantics except in the current (leap) era.
> Does this change if leaps are removed in the future.  For the
> past.  We need a reliable clock, which is TAI to me, and we need
> the leap second table in order to generate graceful dates in the
> past.  Here it is usr/share/zoneinfo/leapseconds, and it expires
> 2023-06-28 ... UTC.
> 
> Just my one cent.
> 
> --steffen
> |
> |Der Kragenbaer,                The moon bear,
> |der holt sich munter           he cheerfully and one by one
> |einen nach dem anderen runter  wa.ks himself off
> |(By Robert Gernhardt)
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