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