In message , at 17:28:52 on
Sat, 21 Aug 2004, Peter Sumner
remarked:
The official time in the UK is maintained by the NPL and it ticks
atomic seconds in UTC.

This is *a* time that is maintained by the NPL.

This is what happens in practice as you can tell by the addition of
leap seconds, which show plainly as an extra 'pip' in the time signals.
If we were using GMT these leap seconds would not be required. For
pedants there is a good explanation at
http://www.npl.co.uk/time/leap_second.html.

And even more detail at:

http://www.wordiq.com/definition/Universal_Time:

Our legislators have mistakenly ignored this and still pretend that
GMT is in use.

Whether a mistake or not, the fact they have ignored the need to make a
change means that Official Time is still UT1.

Not that the maximum error of 0.9 sec makes much difference to the man
on the Clapham omnibus

We can at least agree that 0.9sec is the biggest difference between the
various times.
--
Roland Perry

On Sat, 21 Aug 2004 19:25:01 +0100, Roland Perry
wrote:

In message , at 17:28:52 on
Sat, 21 Aug 2004, Peter Sumner
remarked:
The official time in the UK is maintained by the NPL and it ticks
atomic seconds in UTC.

This is *a* time that is maintained by the NPL.

NPL say http://www.npl.co.uk/time/ "Home of the nation's atomic time
scale" and "providing the UK time scale related to UTC ", in both
cases its "the" time scale rather than just "a" time.

--
Peter Sumner

In message , at 11:32:43 on
Sun, 22 Aug 2004, Peter Sumner
remarked:
NPL say http://www.npl.co.uk/time/ "Home of the nation's atomic time
scale" and "providing the UK time scale related to UTC ", in both
cases its "the" time scale rather than just "a" time.

But go on to say:

"Universal Time (UT) now has three separate definitions (UT0,
UT1, UT2) depending on which corrections have been applied to
the Earth's motion. Authorities are not agreed on whether GMT
equates with UT0 or UT1, however the differences between the two
are of the order of thousandths of a second.

Meanwhile, they are wrong to imply that UTC is the legally accepted
time; unless someone has deliberately "dumbed down", for their Homepage,
the choice between UT0/UT1 and called that UTC.

--
Roland Perry

On Sun, 22 Aug 2004 20:33:16 +0100, Roland Perry
wrote:

In message , at 11:32:43 on
Sun, 22 Aug 2004, Peter Sumner
remarked:
NPL say http://www.npl.co.uk/time/ "Home of the nation's atomic time
scale" and "providing the UK time scale related to UTC ", in both
cases its "the" time scale rather than just "a" time.

But go on to say:

"Universal Time (UT) now has three separate definitions (UT0,
UT1, UT2) depending on which corrections have been applied to
the Earth's motion. Authorities are not agreed on whether GMT
equates with UT0 or UT1, however the differences between the two
are of the order of thousandths of a second.

Meanwhile, they are wrong to imply that UTC is the legally accepted
time; unless someone has deliberately "dumbed down", for their Homepage,
the choice between UT0/UT1 and called that UTC.

Yes, but the difference between the different UTs is not relevant is
it. UTC is currently about 500msec away from UT1 and the difference is
changing as we speak. UT0 varies from UT1 according to where you are
on earth, UT2 and UT1r are smoothed versions of UT1. UTC advances
smoothly, a handy feature for measuring intervals - UT does not.

UTC is the time we use in the UK, our computers, our clocks and our
timetables all use it. Legislation still refers to GMT and this
introduces an ambiguity. Does getting to the legal time mean
correcting the time shown on the most accurate clocks we have?

I can't see any dumbing down on the NPL pages - where do you see this?

--
Peter Sumner

In message , at 22:11:13 on
Mon, 23 Aug 2004, Peter Sumner
remarked:
Meanwhile, they are wrong to imply that UTC is the legally accepted
time; unless someone has deliberately "dumbed down", for their Homepage,
the choice between UT0/UT1 and called that UTC.

Yes, but the difference between the different UTs is not relevant is
it. UTC is currently about 500msec away from UT1 and the difference is
changing as we speak. UT0 varies from UT1 according to where you are
on earth, UT2 and UT1r are smoothed versions of UT1. UTC advances
smoothly, a handy feature for measuring intervals - UT does not.

UTC is the time we use in the UK, our computers, our clocks and our
timetables all use it. Legislation still refers to GMT and this
introduces an ambiguity. Does getting to the legal time mean
correcting the time shown on the most accurate clocks we have?

Yes, unfortunately. Thankfully, there are few *legal* reasons for
knowing the time that require high precision. As this is uk.transport,
one could refer to the "10 minutes" by which trains are officially
counted as late as an example.

I can't see any dumbing down on the NPL pages - where do you see this?

Well, if you don't believe that their use of "UTC", as discussed, on
their home page is "dumbing down", then it's simply a mistake. I was
giving them the benefit of the doubt, ymmv.

The obvious thing for them to do is to briefly discuss the tensions
between the law, UT1, their clocks and UTC.
--
Roland Perry