M. Warner Losh
imp at bsdimp.com
Fri Sep 3 15:19:47 EDT 2010
In message: <7A21EAEC-BB0A-4966-A8DB-86B084DF0963 at batten.eu.org>
Ian Batten <igb at batten.eu.org> writes:
: > do we
: > have enough of a community of |DUT1| < 1s to justify the costs to the
: > rest of the world, or is it time that this crowd shoulder the costs of
: > the raw data they need?
: Of course, one issue is that it's not a matter of |DUT1|<1s, but
: having DUT1 at all. The formats by which DUT1 is propagated in time
: signals deeply assume <1, so if it became >1 it couldn't be propagated
: in those signals. Which means that any and all equipment that
: consumes it is instantly broken, as it can't recover UT1. Even if the
: format could accommodate >1, of course, one assumes that almost all
: sane implementations would sanity check the value of DUT1 to confirm
: it's <1, so would reject the larger value anyway.
: You could modify the format, but you'd have to do so in a way which
: didn't then break all the equipment that wants UTC but pokes around in
: the extra data to recover the date, or the summer time indicator, or
: whatever. And it would involve replacing all the UT1 equipment
: I don't know, and I suspect the ITU don't either, how much (if,
: indeed, there is any) equipment is currently consuming the DUT1
: portion of the national time standards, and why.
I think that this is why the leap second proposals say they won't
disseminate DUT1 anymore. All they really mean by that, I think, is
that we'll measure it, we'll pubish it, but the time broadcasts will
reset it to '0' and users should note that it isn't available that way
I lump all the gear that (a) needs to know about it and (b) does
something with it in the same boat. There is a danger here, however
if the (b) is display it to the user who then doesn't know that
something is amiss and believes '0'.
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