[LEAPSECS] comp.risks post in need of response

[M. Warner Losh]

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