[tz] Fractional seconds in zic input

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Mon Feb 5 22:32:06 UTC 2018

On 2018-02-04 22:59, Steve Allen wrote:
> On Sun 2018-02-04T21:07:54-0800 Paul Eggert hath writ:
>> It's not clear to me that the zic man page should specify how much precision
>> is intended to be significant.
> At the 10th plenary assembly of the CCIR in 1963 Rec.  374 specified
> that radio broadcast time signals should be within 100 ms of the
> intended correct time.
> At the 12th general assembly of the IAU in 1964 Commission 31 (Time)
> reported that radio broadcast time signals permitted worldwide
> synchronization to within 2 ms.  But the tabulated differences of time
> signals published by the BIH show that not all broadcasts were
> achieving the 100 ms target.
> At the 11th plenary assembly of the CCIR in 1966 Rec. 374-1
> still specified 100 ms as the time offset.
> At the 12th plenary assembly of the CCIR in 1970 Rec.  460 specified
> the use of leap seconds offset from without placing any limit on the
> offset.
> It was not until the 13th plenary assembly of the CCIR in 1974 July
> that Rec. 460-1 specified that the signals should not deviate by
> more than 1 ms.  The date for this to become effective was 1975-01-01.
> So fractional second offsets in tz with a precision any smaller than
> 1 ms are already beyond the level of technical conformance which was
> being achieved by the broadcasts that served as the basis of legal
> time for various jurisdictions at 1970-01-01.

Have the ITU not dropped those requirements?
Digital production and distribution systems introduce many ms to s delays in
broadcast time signals, even non-FM BBC stations, and many stations are off UTC
by seconds from higher precision sources like NTP and GPS.
Only the few dedicated national standard time broadcasts left seem to be within
those limits, after correcting for distance and path delays.

Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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