[ntp:questions] Timing GPS recommendations

Chris Albertson albertson.chris at gmail.com
Tue Aug 21 06:30:32 UTC 2012

Actually can CAN set a remote clock very accurately.  This is how NTP works
and what it idoes best.    NTP uses the Internet to synchronise clocks to
MUCH higher precision than the delay in Internet messages.

Try this:  You try to adjust the rate of an old mechanical clock by
adjusting a screw that says "faster/slower".  But your "reference clock" is
across the street and you have to walk back and forth.   This can actually
work very well if you can wait a few months.   First you walk across the
street and back and measure the time it takes.  Do this many times and keep
the mean and sigma.  Now you can set your clock to what you read on the
reference clock but add in 1/2 the mean round trip time.   Now wait 100
days.   Go and read the reference clock and come back add 1/2 the mean and
note the error.  Let's say your clock gained one minute.   Now you know the
rate of your clock relative to the standard to better then one part in
100,000.  We adjust the screww to remove some fraction of the observed
error.  Then we wait aother 100 days and do it again.  Eventually the error
in the rate gets small.    NTP uses this same method but repeats it
thousands of times.

The accuracy with which you can set your remote clock by walking down the
street depends on measuring the mean time to wak down the street.  But we
are using a computer so measure many tests

On Mon, Aug 20, 2012 at 12:17 PM, unruh <unruh at invalid.ca> wrote:

>  Imagine that you have a wristwatch
> that is accurate to the second but your send out messangers by foot to
> deliver the time to your friend across town. Do you really think that
> buying a new wrist watch is the way to improve the time your friend
> gets?

Chris Albertson
Redondo Beach, California

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