[LEAPSECS] Straw men

[Ian Batten]

On 10 Jan 2012, at 1959, Clive D.W. Feather wrote:


> Ian Batten said:

>> You cannot set up a bijection between successive 1s timestamps of UTC and successive valid 1s timestamps of UK Civil Time, because the civil timestamps between 01:00:00 and 02:00:00 on the fourth Sunday in October each map to two distinct UTC timestamps, as they are repeated in the sequence of UK Civil timestamps.  Therefore UK Civil time is not mean solar time.

> 

> (1) I'm not convinced that's correct, since there's an implied labelling of

> whether any given timestamp is in "the period of summer time" or not.


I'm not convinced either way, so I'm just throwing out ideas.  I don't think there is an implicit labelling, or if there is, I don't think it's applied consistently or accurately. 


> 

> Note that, in the Act, "the period of summer time" is defined using GMT at

> both ends. So the last timestamp is 02:00:00, but that is implicitly

> "summer time" since it's defined as being the last one because it is "one

> o'clock, Greenwich mean time".


In that scenario, it would be impossible to determine which of two points in time 60 minutes apart were intended.  So the two systems have to be distinguished in the documentation for the change over point: in the Autumn, there are two 02:00:00s (or, more accurately, 02:00:00 is followed once by 01:00:01 and once by 02:00:01).


> 

> (2) Not last year. The fourth Sunday in October was the 23rd. BST ended on

> the 30th.


My mistake: I had in mind that the Summer Time Act was last and the 9th EC Directive was fourth.  In fact, as you point out, it's the other way around: the UK used to be fourth, but now it's last in line with the EU.  Nigel carefully chose "second Saturday" for his bbq to avoid this :-)  I don't think it affects my argument.

ian