Re: the tail wags the dog

From: M. Warner Losh <imp_at_BSDIMP.COM>
Date: Sun, 22 Jan 2006 21:43:29 -0700 (MST)

In message: <0601222150.AA13090_at_ivan.Harhan.ORG>
            msokolov_at_IVAN.HARHAN.ORG (Michael Sokolov) writes:
: Steve Allen <sla_at_UCOLICK.ORG> wrote:
:
: > The CGPM recommendation on the timescale everyone should use says UTC.
: >
: > UTC(insert your national time service here) is available in real time.
: >
: > TAI is the mathematical (really the political or diplomatic) entity
: > upon which UTC is ostensibly based, but the practical and legal
: > reality is the other way around.
:
: Has it occurred to any of you that *THIS* is the very root of the problem,
: that *THIS* is what we need to change?

I believe so.

: Also, isn't TAI readily available in real time from GPS? (How difficult
: can it be for the routine parsing the data stream from the GPS receiver
: to add 19?) OK, OK, it'll be TAI(GPS) rather than "true TAI", but then
: your UTC is really UTC(NIST) or UTC(USNO) or UTC(PTB) or whatever rather
: than "true UTC".

You can get an excellent approximation of TAI from GPS, assuming that
you use a sane receiver... Some firmware doesn't deal well with
reporting the raw, uncorrected GPS time, but many do it well.
Depending on your needs, you may have to put the GPS receiver into a
mode that only reports URC... Well, you get the idea. It can be done
to a degree of accuracy that most people will accept, but the
post-processed time scale calculations are a little better than what
happens in real time.

Warner
Received on Sun Jan 22 2006 - 20:46:18 PST