[LEAPSECS] What's the point?

Clive D.W. Feather clive at davros.org
Tue Feb 15 05:05:36 EST 2011

Poul-Henning Kamp said:

>> The UK's standard time broadcast, which is funded by the government,

>> contains DUT1 in a format which doesn't permit |DUT1|>0.9. Whatever

>> people argue (rightly) about the de facto legal time in the UK being

>> UTC, the de jure legal time is "GMT" which is taken to be UT1.


> Where and by who is that "taken to be UT1" ?

Just about everyone. Since GMT well predates the invention of UTC, it can't
be anything other than UT, UT1, or UT2.

> Just because the additional DUT information is broadcast is no guarantee

> that any decodes it and uses it.

True but irrelevant.

> And I certainly do not see a DUT offset between NTP servers in the

> rest of the world and NTP servers in the UK.

Because those NTP servers provide UTC-with-leap-second-issues, not UT1,
just like the ones in the rest of the world.

Curiously enough, NTP is *NOT* the definition of legal time in the UK.

> You will need to document this claim before anybody will buy it,

Which one? That GMT = UTC? That legal time is GMT?

> and I am quite sure that if you can, a lot of people will be

> very surprised...

Well, as to the latter, the 1978 law says:

| Subject to section 3 of the Summer Time Act 1972 (construction of

| references to points of time during the period of summer time), whenever an

| expression of time occurs in an Act, the time referred to shall, unless it

| is otherwise specifically stated, be held to be Greenwich mean time.

This is almost certainly a tidying up of older legislation in the same
wording, but I don't have quick access to that.

The Summer Time Act 1972 says:

| 1(1) The time for general purposes in Great Britain shall, during the

| period of summer time, be one hour in advance of Greenwich mean time.

| (2) The period of summer time for the purposes of this Act is the period

| beginning at one o'clock, Greenwich mean time, in the morning of the last

| Sunday in March and ending at one o'clock, Greenwich mean time, in the

| morning of the last Sunday in October.


| 3(1) Subject to subsection (2) below, wherever any reference to a point

| of time occurs in any enactment, Order in Council, order, regulation,

| rule, byelaw, deed, notice or other document whatsoever, the time referred

| to shall, during the period of summer time, be taken to be the time as

| fixed for general purposes by this Act.

| (2) Nothing in this Act shall affect the use of Greenwich mean time for

| purposes of astronomy, meteorology, or navigation, or affect the

| construction of any document mentioning or referring to a point of time in

| connection with any of those purposes.

The 1954 legislation for Northern Ireland says:

| Words in an enactment relating to time and references therein to a point of

| time shall be construed as relating or referring to Greenwich mean time,

| subject, however, to any statutory provision which may for the time being

| provide that, during any specified period or periods, time in Northern

| Ireland is to differ from Greenwich mean time.

Clive D.W. Feather | If you lie to the compiler,
Email: clive at davros.org | it will get its revenge.
Web: http://www.davros.org | - Henry Spencer
Mobile: +44 7973 377646

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