I had two machines running Lady Heather with the singing chime clock mode
enabled (that plays a chant from the Missa Assumpta on the quarter hours).
One machine was connected to a Ublox Neo-6M receiver and another to a Z3801A.
I noticed that the two machines sang their jaunty monk tunes offset by around
one second. Since a man with two singing GPS clocks never knows what time it
is, I replaced the Z3801A with a Jupiter-T and the two clocks were still out
of sync. Finally I tried Motorola M12+ and UT receivers and the same thing
happened. It looks like the Ublox time is ahead by a second compared to all
the other receivers. I then specified a -1 second "rollover" correction to
the Ublox machine and the two clocks sang in perfect harmony. Has anybody
noticed such behavior with other receivers?
BTW, note that the Ublox binary time message has a "fractional nanoseconds of
the seconds field" (+/- 500,000 nanoseconds) correction that must be applied to
the hrs:min:secs values (which I am doing). The fractional time offset forms a
sawtooth with around a 120 second period. Attached is a GIF... white is the
nanosecond fractional time offset. Magenta is the receiver estimate of its
time error (both in nanoseconds). The Trimble Resolution-T receivers report a
similar "local clock bias" value, but they don't seem to document what it
actually is...
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