On Nov 2, 5:23*am, 309 wrote:
Well, it's time to set clocks back...and I noticed something
interesting today.

My VolksLogger's clock seems to run 15 seconds ahead of other GPS
units

I say the VL seems ahead...and this is based on seeing the minute
readout roll over ahead of the other GPS units...since the VL display
doesn't show seconds.

It will show seconds, though, on the IGC file. What would be useful
would be to borrow another IGC-approved recorder and run the two
recorders together on a flight or a drive in a car. Make some
manouevres that can be identified post-flight (or press the Pilot
Event buttons at the same time) and compare the times in the IGC
files.

As others have said, your 15 seconds is very close to the 14 leap
seconds that have been added to UTC since January 2000 when the US GPS
system first came on line. Internal GPS system time is still UTC as
in January 2000 and GPS units normally automatically make the 14
second correction so the difference is not (normally) noticed by
users.

It would be interesting to hear the result of a comparative test with
another GPS recorder.

BTW, the Russian GLObal NAvigation Satellite System (GLONASS) system,
their equivalent of the US GPS, corrects its internal system time to
UTC every time a leap second is added by international agreement,
normally at midnight on 31 December. But that means that GLONASS has
to be taken off line while all its electronic clocks are re-set.
Question, does anyone know how long this system reset takes? It would
be embarrassing if you were half way down a bad-weather GLONASS
approach at the time.


Ian Strachan
Lasham Gliding Centre