[LEAPSECS] nails in the coffin of mean solar time

[Rob Seaman]

On Jun 15, 2007, at 1:57 PM, Poul-Henning Kamp wrote:


> However, for the approx 200 computers I have in my personal sphere

> of influence, I can in less than 1 second split them into these two

> categories:

>

> 1. Does this computer care if there ever is another leap-second ?

> 	199

>

> 2. Does this computer care if civil time is aligned with earth

>    orientation ?

> 	1


Yes, yes - operating systems and embedded hardware are one place to  
look for DUT1 (Y2K-like) dependencies.  So too are applications,  
library code, interface definitions, GUIs, network dependencies.   
This particular discussion was started with concerns about DoD  
assets.  Might modules, interfaces, libraries, implicit data  
structure interdependencies, human factors, operating procedures and  
so forth comprising the system of systems that is a ballistic missile  
submarine, or cruise missile, or Pacific fleet operations require  
that heretofore negligible DUT1 corrections be interposed?

Both logic and prudence suggest yes.  Having invested in such a USN  
or DoD or NASA wide inventory, one will either discover that  
(unlikely as I believe it to be) no code or operational changes are  
needed - or that changes are indeed needed.  If changes are needed,  
the updated systems will require lengthy and expensive formal  
testing, integration, deployment.  But perhaps less obviously, even  
if no changes are deemed necessary an open-ended regime of testing  
and retesting will also be needed to uncover any Y2K-like issues  
triggered as DUT1 grows secularly and crosses code-dependent  
boundaries.  Effects will be subtle to discover, but perhaps - umm -  
"dramatic" in their implications.

And can you really be so confident that 99.5% of your systems are  
100% free of any possible DUT1 related issues?  Microsoft can't even  
get daylight saving time correct.  We've already established that  
different countries rely on different legal notions of time.  Do your  
computers talk to any that reside in other countries?

The bumper sticker bottom line:

	Absence of evidence is not evidence of absence.

Rob Seaman
NOAO