[tz] [PROPOSED 2/3] Simplify leapadd

Michael H Deckers michael.h.deckers at googlemail.com
Wed Jan 15 23:50:34 UTC 2020

    On 2020-01-15 15:53, Steve Allen wrote:

> The original version of CCIR Rec. 460 did not specify any bound.
> See volume 3 page 227
> http://search.itu.int/history/HistoryDigitalCollectionDocLibrary/4.278.43.en.1004.pdf

    I see - that version of Rec 460 does not even say when
    leap seconds may be introduced. But it references
    "detailed instructions" (which is Report 517) for its
    implementation, so I assume both documents applied to UTC
    since 1972-01-01. This is corroborated by Rec 374-2
    (on p 222 of that volume).

> The technical details with max 0.7 second deviation came from Report
> 517 which was not forged until 1971 February and included into the
> CCIR volume 3 as addendum starting on page 258a.  That 0.7 limit was
> disregarded in less than two years also due to Soviet political
> pressure, leading to a rewrite that gave the limit of 0.8 second even.
> though the 0.7 limit had already been hard-coded into the format of
> the broadcast time signals.

    My historical knowledge is too weak to let me understand the
    political ramifications. But apparently the second leap second
    insertion prescribed by the BIH already violated the 0.7 s bound:
    the difference UT1 - UTC was about +0.81 s on 1973-01-01 (after
    the leap).

    So I find it quite plausible that the bound for |UTC - UT1|
    was soon increased to 0.9 s (while |DUT1| is required
    to be <= 0.8 s) -- even without the political pressure.

    Michael Deckers.

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