Re: [LEAPSECS] Risks of change to UTC

From: John Cowan <>
Date: Fri, 20 Jan 2006 15:12:15 -0500

Rob Seaman scripsit:

> Only a minority (small minority, one would think) of
> systems currently include any DUT1 correction at all - although these
> will perhaps tend to be the most safety-critical applications. [...]
> That is, of course, one of the major issues for astronomers - we rely
> on UTC providing a 0.9s approximation to UT1 and most of our systems
> don't use DUT1. Even our high precision applications (in either
> interval or universal time) don't tend to require conversions other
> than as a preprocessing step. Remediating our systems for such a
> fundamental change to UTC would involve much larger changes than Y2K
> did - algorithms and data structures would have to change, not just
> the width of some string fields and sprinkling some 1900's around.

I don't understand this. The first class of applications, those
that actually receive DUT1 from somewhere, probably have a hard-coded
assumption that |DUT1| never exceeds 0.9s or at worst 1.0s. They would
need remediation. The second class, which just assumes UTC = UT1
and doesn't care about subsecond precision, would simply need to be
front-ended with a routine that got DUT1 from somewhere and mixed it
with TI to generate their own UT1. This is technically remediation,
but of a rather black-box kind.

> Also, standalone applications would have to become network aware to
> have access to externally derived tables of DUT1.

Well, this is perhaps no worse than systems that now have access to UTC
and want reliable interval time needing externally derived tables of
leap seconds.

> Astronomers might be unusual in needing to introduce DUT1 into our
> systems (on a short schedule for a large expense) should Sauron win
> and the nature of UTC change, but we wouldn't be alone. And as clock
> time diverges further and further from solar time, more systems in
> more communities (transportation, GIS, innumerable scientific
> disciplines, what have you) would be revealed to need remediation.

Can you spell out some of those implications?

What has four pairs of pants, lives             John Cowan
in Philadelphia, and it never rains   
but it pours?                         
        --Rufus T. Firefly            
Received on Fri Jan 20 2006 - 12:12:38 PST

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