On Sat, 19 Aug 2000, Rob Seaman wrote:
> The question is whether current ephemeral technical
> issues will direct both the choice of solution and the pace of its
> implementation.
Do you mean "ephemeral" in the usual sense of "lasting for a short time
only", or in the technical sense "pertaining to an ephemeris"? The
context suggests the former.
> > The trouble is that many systems cannot "download" the magnitude, as
> > they are not on line. Just think about all the different clocks there
> > are in the world in various embedded systems ranging from microwaves to
> > cars. In general, we do not care about errors in the clocks on these
> > systems, as they are used only by humans, but in a future version this
> > might not be the case.
>
> I'm struct by the phrase "used only by humans". GPS is used only by
> humans. GLONASS is used only by humans. Apparently the spread spectrum
> community has problems handling leap seconds. Who cares about spread
> spectrum technology beyond humans?
Who, in all this wide universe, cares about *anything* except humans,
as far as we know?
I meant of course "used only by people who only care about what time
it is to an accuracy of a few minutes or so" as distinct from systems
that will malfunction if they do not know civil time to the nearest
second or better. Most of us don't expect accurate time from our microwaves.
> Well, it's suggested that emerging technologies have intrinsic
> difficulties handling leap seconds. Now apparently it's only "some"
> emerging technologies - and they aren't really "emerging" at all, make
> that "interim" - but are the difficulties intrinsic? That's the real
> question.
All technologies whatever are "interim", I think.
> What fundamental timing complications occur due to leap seconds?
There are no *fundamental* timing complications. We *could* adapt to a
system in which the length of the hour varies with the date, as the
whole of Western culture did until mechanical clocks were invented..
All is a matter of convention.
However, the notion that the number of seconds in a year can't be
predicted a year in advance makes for *practical* timing complications.
> That is - what fundamental complications that wouldn't be more
> appropriately addressed by merely selected an unsegmented time scale
> like TAI for that project in the first place? It worked for GPS, why
> not for the other guys? After all - these are highly technically trained
> (and highly economically advantaged) folks - why should everybody else
> (literally "everybody else for the rest of time") be expected to
> accommodate them?
As a practical matter, most timepieces (other than sundials) are set
using local civil time, which is slaved to UTC, but then they tick
minutes with exactly 60 seconds in them each, until the next time someone
has a practical reason to reset the clock, like power failure or
(if the device is primitive enough) DST transition.
A more sophisticated device could be set up to reckon 61 seconds
in certain minutes, provided those minutes were predictable in advance.
Even a wall clock or a watch could be programmed to do that at small cost.
But do you really foresee a future in which every wall clock and watch is wired
so that it can download the leap seconds from the Internet? That
is just too techno-optimistic for me to swallow.
--
John Cowan cowan_at_ccil.org
C'est la` pourtant que se livre le sens du dire, de ce que, s'y conjuguant
le nyania qui bruit des sexes en compagnie, il supplee a ce qu'entre eux,
de rapport nyait pas. -- Jacques Lacan, "L'Etourdit"
Received on Sat Aug 19 2000 - 22:38:59 PDT