Re: [LEAPSECS] Schreiver AFB warns about leapsec

From: Rob Seaman <>
Date: Tue, 20 Dec 2005 03:46:48 -0700

On Dec 20, 2005, at 1:30 AM, Poul-Henning Kamp wrote:

> There is an interesting PowerPoint (sigh...) at Schriever AFB's GPS
> support center:
> Leap_Second_Event.ppt

Agreed. Very interesting.

> They clearly know what the problem with leap seconds is :-)

Agreed, although they simplify leap seconds as being:

        - Needed to compensate for changes in earth’s rotation

Suggest folks read the entire presentation, which delivers common
sense advice without editorial comment. (That's our job.) The
authors start by assigning the responsibility appropriately:

        - User’s realization of UTC could incorrectly step by one second

They describe limits to the affected systems:

        - Leap second should not affect stand alone navigation or
positioning (affects timing output of receiver)
        - Adjustment transparent to users with GPS receivers in compliance
with IS-GPS-200
        - Some receivers may require manual adjustment by users
        - Systems (military, civil, commercial) using GPS timing with a
tolerance less than 1 second, might be [emphasis in original]
impacted if leap second adjustment is not made properly (either
automatically or manually)

A hint that the issue may be more complicated than it appears:

        - Often, use of GPS timing in embedded systems is difficult to
discern – consult your system engineers / experts

An interesting observation:

        - Leap second occurs at an awkward time - New Years Eve

Maybe obscurity in scheduling and implementation is not a desirable
characteristic after all. Perhaps the problem would "solve itself"
through market forces if leap seconds were simply required to occur
on normal business days at 9:00 am EST, just in time for the opening
of the NYSE.

...and they deal with the consequences pragmatically, rather than
trying to legislate physical reality out of existence:

        - Contact your UE manufacturer to determine if your UE is IS-
GPS-200D compliant with respect to leap seconds
        - Ensure documentation, procedures and personnel are in place to
deal with potential problems
        - Monitor your system through the leap second event
        - Report if you have problems
        - We need to document so we can correct the problem for next event

In addition to pondering how well such preparations would succeed for
events three orders of magnitude larger occurring only every several
centuries, this reader is left wondering what the corresponding
presentation would look like if it were describing remediation to the
same systems to support DUT1 > 0.9s.

Rob Seaman
National Optical Astronomy Observatory
Received on Tue Dec 20 2005 - 02:47:46 PST

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