On 12 Apr 2011, at 00:48, Tony Finch wrote:
> On 11 Apr 2011, at 20:19, Gerard Ashton <[email protected]> wrote:
>
>> If leap seconds are abolished, and Britain decides to maintain an
>> approximation
>> to mean time 0 degrees longitude, +/- a fraction of a second (modulo time
>> zones, as currently defined),
>> over time the difference in timekeeping systems will become clearly
>> perceptible and clearly
>> distinguishable to people with no special equipment beyond a carefully set
>> wrist watch.
>
> But note that Britain does not currently have the capability to maintain GMT
> since the relevant department was closed decades ago and the institution that
> housed it was abolished. If the international consensus is to change UTC then
> UK civil time will have to follow.
I think it's messier than that. De facto UK time is UTC, as we've discussed,
but the only source of de jure legal time now is MSF: it broadcasts UTC(NPL),
but DUT1 is available in the payload (and that's (UT1-UTC), not (GMT-UTC),
because as you say GMT is unmaintained). So of itself, the non-maintenance of
GMT hasn't affected anyone, as the (UTC, DUT1) pair analogue If UTC were
unhitched from UT1, the MSF format couldn't carry |DUT1|>0.9, but let's imagine
that was resolved somehow for the small community of users to whom it matters:
a DUT1-like quantity would be available. So if there were applications for
which something very close to GMT were needed, it would be no less available in
the future than it is today.
However, a lot of UTC clocks (either NTP or MSF) have been sold as "UK Legal
Time" clocks, for trading and banking systems, and so long as DUT1 is small
that doesn't really matter: it's hard to imagine a real legal action (as
opposed to some geek's fantasy) revolving around quantities less than a second.
And for those scenarios where it might matter, the solution is easy. The
Interpretation Act 1978 S.9 has nothing to say about contracts, so case law,
"reasonable man" tests and so on would resolve the first action, and thereafter
contracts would add "times in this contract shall be assumed to be UTC" to the
definitions section. Wise lawyers might add that clause anyway. Unless
someone can produce something other than the Interpretation Act, "uk civil
time" is only GMT insofar as it affects the interpretation of primary
legislation which does not specify another timescale, and even then (the thing
engineers do badly when assessing UK law) case law is almost certain to
override it.
The NPL/BIS document someone posted to this list a few months ago included a
comment about the political difficulties of formally changing GMT. They're
right: an unstable coalition government with a profoundly Euro-sceptic wing
(this would smack of "Brussels" and "gold-plating", even though it's obviously
neither) and a desire to remove regulatory red-tape is hardly going to pass
legislation which on the face of it affects everyone with a clock, even though
in fact it makes everyone's lives easier (UTC is ubiquitous, processing DUT1
isn't). So in the grand British tradition of compromise and fudge, UK Legal
Time would converge on whatever was most easily available, without any primary
legislation being needed.
ian
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