Re: Web page updates following recent discussions

[Gary E. Miller]

Yo David!

On Tue, 19 Jan 2021 09:50:25 +0000
David Taylor <gm8arv@yahoo.co.uk> wrote:

> On 18/01/2021 19:55, Gary E. Miller wrote:
> > Your sysem clock is much more stable than your RTC.  Why have a
> > terrible RTC discipline your not so bad system clock?
> > 
> > The RTC is for when the system is off, After discipling by the
> > system clock.
> > 
> > RGDS
> > GARY  
> 
> Yes, but there are some circumstances where an Internet connection is 
> never going to be available out in the field, and then you will get
> the time of day from the RTC, and the system will drift thereafter
> according to its own clock.

Two clocks here.  The RTC clock and the system clock.  The system clock
is more accuratet than the RTC clock.  So you do not want NTP
to adjust the system clock to match the RTC clock.  Bass ackwards.

>  I would like to measure how far such a
> system drifts from its initial setting in such circumstances.

The RTC has tools for that.  NTP has tools for that.  ntpviz knows all.

> Mind you, from the RV3028 specs if the chip is at room temperature
> you could be looking at well under 10 ppm, so in the order of a
> second a day.

Which is much worse than the system clock.  I just looked at one of mine
0.67 ppm.  Much better than the RTC 

And temperature sensistive is a huge topic in itself.  Some, including
myself, have gone to great lengths to temperature stabilize the RasPi
clock.

> If there are references to similar measurements I would appreciate
> knowing.

There has been lots of earlier discussion on this with ntpviz providing
read data.  I suggest you setup ntpviz and collect real data.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

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