[LEAPSECS] comp.risks post in need of response

Rob Seaman seaman at noao.edu
Tue Dec 9 15:14:40 EST 2008

Our (familiar) views are rather orthogonal to the comp.risks assertions.

On Dec 9, 2008, at 10:50 AM, M. Warner Losh wrote:

> In message: <B2C1F790-303D-4E34-BB66-F8E7B4319D00 at noao.edu>

> Rob Seaman <seaman at noao.edu> writes:

> : Anybody want to volunteer to take a wack at setting the nice folks

> at

> : the Risks Digest straight regarding a timekeeping issue?

> :

> : http://catless.ncl.ac.uk/Risks/25.47.html#subj12

> :

> : I'm sure someone from any of our various philosophical encampments

> : would do a fine job of telling them why "NominalDiffTime" is a silly

> : idea. If only the claim were true, however:

> :

> : "If you don't care about leap seconds, use UTCTime and

> : NominalDiffTime for your clock calculations, and you'll be fine."

> :

> : Certainly nobody who does need to recover accurate UT1 from civil

> time

> : is going to trust this library.


> You can't recover UT1 from Civil Time.


> Before you crawl my case for that statement, let me explain.


> First, if you need to know UT1, you have to get it from somewhere on

> the net. It isn't broadcast in any meaningful way today (.1s isn't

> meaningful).


> Second, if you are doing real time thing where UT1 is important,

> you'll need some source of timing signals to do the real time thing

> you need to do. In that case, you are getting time directly from GPS

> or some other form of time exchange.


> If you are going to that level of effort, then you already know the

> difference in the different time scales.


> Warner

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