[LEAPSECS] BBC radio Crowd Science

[Brooks Harris]

On 2017-02-01 07:39 AM, Steve Summit wrote:
> Brooks Harris wrote:
>> On 2017-01-31 08:21 PM, Steve Summit wrote:
>>> I feel like I should apologize for my earlier contribution to it,
>>> which presented a nice-looking, persuasive-sounding argument
>>> which now looks an awful lot like it's... wrong.
>> Not at all. Its an informed contribution. And I think it's not "wrong".
>> At least not yet. I think its "right", so far.  :-)
> On further reflection, I think we're all right.  For every
> let's-look-at-the-arithmetic argument that suggests we should
> use the "new" offset during the leap second, I can come up with
> one which suggests the opposite.  (Basically it depends on
> whether you come at the leap second "from below" or "from above".
> I'll send the longwinded details in a separate message, if anyone
> actually cares.)  So I'm right, and you're right, and Warner's
> right, and Steve Allen is especially right in his assertion that
> it's just inherently, fundamentally ambiguous.

Yes, well its that "fundamentally ambiguous" part that none of us can 
stand and keeps us obsessed with the LEAPSECS discussion, I guess.

I continue to believe TAI-UTC updates after the Leap Second, at the UTC 
YMDhms midnight rollover. Digging deeper, and once again reading Rec 460:

https://www.itu.int/dms_pubrec/itu-r/rec/tf/R-REC-TF.460-6-200202-I!!MSW-E.doc

Section C Coordinated universal time (UTC) says "UTC is the time-scale 
maintained by the BIPM, with assistance from the IERS..."

This says BIPM is the authority that maintains the UTC timescale, 
doesn't it?

Section E DTAI says "... The TAI - UTC values are published in the BIPM 
Circular T ...".

OK, so, better look more carefully at Circular T.

CIRCULAR T 348    ISSN 1143-1393
2017 JANUARY 10, 10h UTC
ftp://ftp2.bipm.org/pub/tai//Circular-T/cirthtm/cirt.348.html

And there we find - "1 - Difference between UTC and its local 
realizations UTC(k) and corresponding uncertainties. From 2015 July 1, 
0h UTC, TAI-UTC = 36 s. From 2017 January 1, 0h UTC, TAI-UTC = 37 s."

I think this clearly says TAI-UTC updates on 2017 January 1, 0h UTC, the 
midnight rollover. This time-point is *after* the Leap Second, isn't it? 
And its authoritatively stated by BIPM.

Meantime, IERS Bulletin C says the same thing - "from 2017 January 1, 0h 
UTC, until further notice : UTC-TAI = -37 s"

https://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat

I'm not understanding how this can be interpreted any other way. There's 
nothing ambiguous about it to my reading, and I've had this conversation 
with other good engineers that concur with that reading. It may not be 
convenient for some methods of converting TAI seconds to UTC YMDhms 
representation, but there it is, in black and white, near as I can see. 
It also lines up with all the other IERS Leap Second history data products.

You can't just ignore this because its more convenient. Of course you 
can adjust it internally in a specific implementation as required or 
convenient, in fact you probably need to in some way or other. But the 
data supplied by BIPM and IERS needs to be interpreted consistently, right?

-Brooks