[LEAPSECS] Lets get REAL about time.

[Clive D.W. Feather]

Michael Sokolov said:

> What people like PHK fail to grasp is that a whole ton of applications

> absolutely DO NOT CARE how many Cs-133 transitions happen to occur in

> a given *civil* time interval, all they care about is a bijective

> mapping between their timestamps and *official civil time*.


Agreed.


> Each (micro-)nation should indicate its official time with an analog

> clock (i.e., one with rotating hands, not digital) on the wall of a

> government building specifically to drive the point home that notations

> like 23:59:60 are not acceptable.  This non-scalar notation is the

> real fundamental problem with UTC in my eyes,


Total nonsense.

(Nitpick: it's not non-scalar, it's non-uniform.)

If that were a valid argument, then we wouldn't have different numbers of
days in the month because you couldn't have a day-of-month hand on a clock.
Yet clockmakers and the general public seem to have coped.

If leap seconds were predictable (say they were exactly one every 18 months
for the next century) it would be perfectly practical to build an analogue
clock that had 61 divisions on the dial carrying the second hand, and which
jumped the 60 position in most minutes.


> i.e., they should not pretend to have any relation to time-as-in-physics

> and should merely represents particular points in the course of

> "analog" civil time, i.e., particular angular positions of the

> rotating hands of the official clock on the wall of a government

> building.  An indication that Mary Q. Public's subscription expires at

> 2022-07-25T19:41:42 UT1 is perfectly precise and unambiguous

> regardless of how many leap seconds occur between now and then.


Except:
(1) the notation 2022-07-25T19:41:42 UTC is equally precise and unambiguous
when it happens;
(2) since you don't know how much the earth will slow down in the next 10.5
years, you can't (easily, if at all) build a clock that will rotate the
correct number of times;
(3) neither UT1 nor UTC is civil time (though civil time may be based on
one or the other).


> On the other hand, the *civil* timekeeping requirements can be very

> stringent.  The example of expiration of subscriptions that Keith has

> brought up is a very good one: I like the idea of the moment of

> subscription expiration far in the future being defined very precisely

> *in relation to official civil time*, which for the Republic of New

> Poseidia is currently UT1.


But in the real world it *isn't* that predictable. Let's take that
subscription you mention. Under English law that time - without the "UT1"
tag - would be interpreted as BST, since under the Summer Time Act all
times in July are to be interpreted as BST unless specifically mentioned.
Right now BST means GMT+1 (for some meaning of GMT I'm not going to debate
right now). But perhaps Labour come back into power in 2015 and decide to
move us all to the same time as France and Germany. At which point BST will
mean GMT+2. So never mind the 7 or 8 leap seconds - we can't even predict
duration to within an hour.

And that, I think, matches Tony Finch's point: for many things you don't
care about the interval, you care about the end time in the *relevant* time
zone.

-- 
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