Re: Web page updates following recent discussions

[Gary E. Miller]

Yo David!

On Thu, 21 Jan 2021 10:44:02 +0000
David Taylor <gm8arv@yahoo.co.uk> wrote:

> My simple NTP data is on my Web site, and the MRTG/Perl scripts I
> use. For example:
> 
>    https://www.satsignal.eu/mrtg/performance_ntp.php
>    https://www.satsignal.eu/ntp/NTPandMRTG.html

Your "simple" is my "insufficient".  No temp data, no jitter, no
comparison data, no statistics, no fix data.  Try ntpviz

> Yes, I am trying to measure the RTC without disciplining.  As
> interrupts are not possible I will try polling, recording the time
> when the second digit (or value) changes.

Or, just use "hwclock --update-drift" hen look in /etc/adjtime


> The first problem with NTP reading the RTC may be that once NTP knows 
> about it it may try and discipline it, preventing a long-term 
> measurement,

Which  is why I keep repeating to you: "noselect".

> and the second that the RTC can only be read in seconds,
> so even without the disciplining you might be waiting for many weeks
> for the RTC to be a second off!

Yes, patience is required.

> On making the RPi alone as accurate as possible, some RPI 4B show a
> ppm offset of -9 -11, and -19, so far worse than the RTC.

I'm not exactly sure why yours is more than 10x worse than mine.  I'm
guessing you need to let ntpd run longer to discipline the clock.

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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