[LEAPSECS] h2g2

[Ian Batten]

> Would a continuing objection from China or the UK block adoption?


I am trying to locate a correspondence that I had with the then UK  
science minister in about 1999, asking him to clarify the status of  
Lord Tanlaw's proposed legislation to change UK legal time from GMT to  
UTC, which had a second reading in June 1997 but hadn't (and hasn't)  
made more progress.  My memory is that Lord Sainsbury's response was  
in essence that anyone to whom the difference is important knows the  
difference and defines their timestamps appropriately, and for  
everyone else |UTC-UT1| is small enough that it doesn't matter.

Lord Tanlaw's speech is ostensibly available at http://www.publications.parliament.uk/pa/ld199798/ldhansrd/vo970611/text/70611-10.htm 
, although it doesn't seem to be working properly at the moment and  
you may need to refer to http://webcache.googleusercontent.com/search?q=cache:jVw0KpIyKfYJ:www.publications.parliament.uk/pa/ld199798/ldhansrd/vo970611/text/70611-10.htm 
  --- it's an accurate and masterly set of summaries of the history of  
the UK's continuing use of GMT, and the implications thereof.

Lord Sainsbury was, for practical purposes, right.  Provided the  
difference between GMT and UTC is less than a second, as will  
currently be the case pretty much by definition, then that the UK uses  
de facto UTC and de jure GMT doesn't really matter in areas likely to  
provoke legislative or diplomatic interest.  But were the delta to  
grow, there are increasingly many scenarios where it will matter, and  
the UK would have to choose between UT1 (unmaintained, legal, solar),  
UTC with leapseconds (unmaintained, close enough for most purposes to  
legal and solar) and UTC without leapseconds (maintained,  
progressively more distant from legal and solar).    It's not hard to  
confect scenarios where the choice between two timescales nominally  
thirty seconds apart could be worth quite a lot of money --- railway  
public performance metrics spring to mind.

The rubber would meet the road over the contents of what is broadcast  
by MSF (http://en.wikipedia.org/wiki/Time_from_NPL).  It can only  
encode DUT1 in the range [-0.8, +0.8], and therefore is incapable of  
broadcasting a leap-second-less "UTC" and a usable UT1.  For MSF to be  
unable to broadcast UK legal time would be politically unacceptable,  
and for the "UTC" signal to be different to the one broadcast from  
DCF77 (http://en.wikipedia.org/wiki/DCF77) would cause immense  
confusion.  There aren't any spare bits within the current definition  
of MSF to extend the range of DUT1 without breaking all equipment that  
currently uses the signal.

In the current political climate, attempts to change change UK time to  
match a "foreign" standard which would involve legislative effort and/ 
or significant expenditure on replacing equipment are likely to get a  
fairly dusty reception.   Although unrelated, it would also open up  
the whole "moving the UK to WET" can of worms, which has become  
distinctly toxic because of the implications for Scotland.   Mind you,  
one could imagine, if one had had a couple of glasses of wine, England  
acquiescing to a leap-second-less UTC+1/2 to align with mainland  
Europe while Scotland sticks with UT1, or equally Scotland adopting  
leap-secondless UTC+0/1 to look modern and European, while England  
stays on UT1+0/1 to appease UKIP voters (it's unlikely Scotland would  
accept anything+1/2).

[[ In passing, it's worth noting that the MSF signal deeply embeds the  
idea that all you need to know about in the UK is UTC, DUT1 and a  
single bit indicating summer time.   The signal was inaugurated in  
1950, so double summer time had been stopped, and the trial between  
1968 and 1971 involved staying on summer time all year around.  Were  
the UK to try WET, it doesn't seem possible for MSF to transmit  
anything+2 in any format, so UK-specific equipment that doesn't have  
an hour-offset setting (like my alarm clock) will be hosed. ]]

ian