Re: [LEAPSECS] NOT A cruel fraud!

From: M. Warner Losh <imp_at_BSDIMP.COM>
Date: Sun, 22 Jan 2006 09:22:25 -0700 (MST)

In message: <43D36180.3050706_at_edavies.nildram.co.uk>
            Ed Davies <ls_at_edavies.nildram.co.uk> writes:
: M. Warner Losh wrote:
: > : > TAI is specifically contraindicated as a time
: > : > scale.
: > :
: > : > TAI is not currently recommended by its creators as a viable time
: > : > scale.
: > : >
: > :
: > : These claims are intellectually fraudulent. The archives in fact support
: > : the opposite of what Mr. Losh contends.
: >
: > Actually, it isn't quite that cut and dried.
:
: OK, so why is TAI contraindicated then?
:
: I've been on this list since 2002-07 and not yet seen a good
: argument against it.

The short answer is that you cannot get a time feed of TAI, so the
high precision folks don't like people calling something that's
derived indirectly TAI. TAI(UTC(foo)) can be derived, however, if
you know the current leap offset. This isn't broadcast in many time
formats.

Having said that, our company uses TAI internally for all its time
code and translates on output. Doing that doesn't free you from
knowing about leap seconds, however, since you have to know about them
to convert to/from UTC which is universally broadcast or available.
GPS makes things a little easier, since there's a fixed offset from
TAI, but even it present difficulties because you need the current
leap offset to display UTC times. However, some GPS receivers insist
on doing silly things when you try to get the raw time without
leapseconds. Our systems need to have unambiguous timestamps, as well
as a requirement to display UTC.

Warner
Received on Sun Jan 22 2006 - 08:25:22 PST