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> You are thinking about the difference between GPS (System) Time (which is not
> updated for leap seconds) and UTC which is compensated for leap seconds to
> keep it within 0.9 seconds of UT1. Currently the difference is 13 seconds.
> Nothing to do with "satellite rollover."

I get deeply confused on this subject at times.  My Garmin 76 appears to
display the same time as other online government sources (nanoseconds
between glances at one or the other noted ;-)

Somehow I thought the GPS difference was set back to zero when the
satellites rolled over.  Perhaps my recollection, or source (a GPS list
years ago around the Y2K scare) is/was in error.

I did read at:

http://tycho.usno.navy.mil/gpstt.html

"The number remains constant until the next leap second occurs. This offset
is also given in the navigation (NAV) message and your receiver should apply
the correction automatically. As of January 1, 1999, GPS time is ahead of
UTC by thirteen (13) seconds."

I enjoy the use of the word "should" when dealing in multiple seconds or
nanoseconds. 

If I understand, the II/IIA satellite containing two cesium (Cs) and two
rubidium (Rb) atomic clocks, and Block IIR satellite containing three Rb
atomic clocks all report to a "paper" Composite Clock (CC).  Then some black
box factors in the missed leap seconds and viola, my 76 has the time to the
nearest .9 seconds of some UTx standard.  How does magic work?

Bill

   

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