The Earth's not slowing down fast enough to

Fri Oct 10 18:15:19 UTC 2003

> Date: Tue, 07 Oct 2003 23:33:45 -0700
> Subject: The Earth's not slowing down fast enough to suit Motorola
> 
> Motorola reports that several GPS receivers in its Oncore line will
> misdisplay the date on 28 Nov 2003 at midnight UTC.  For a one-second window
> the receivers will mistakenly report the date as 29 Nov instead of 28 Nov.
> 
> Here's why.  Every couple of years or so for the past three decades, the
> International Earth Rotation Service has announced a leap-second because the
> Earth is rotating slightly more slowly than an 86400-second day would
> suggest.  But since 1 Jan 1999, we've had an unusually long dry spell
> without any leap seconds.  The GPS week number in the UTC correction
> parameter is 8 bits long, which allows for 256 weeks of unambiguous time
> calculation.  Until now this parameter has never rolled over, but because of
> the dry spell 28 Nov will be exactly 256 weeks after the most recent leap
> second, and the rollover will contribute to the bug.
>    <http://www.motorola.com/ies/GPS/docs_pdf/notification_oncore.pdf>
> 
> Steve Allen writes in <http://www.ucolick.org/~sla/leapsecs/onlinebib.html>
> that some JDAM smart bombs and other munitions are rumored to contain these
> receivers.  Anyone intending to use those weapons around the magic window
> might want to reschedule their bombing runs for some other time. ...

	for all you NTP/GPS junkies out there... :)

--bill