Best practices question

Gary E. Miller gem at
Wed Jun 26 18:07:25 UTC 2019

Yo Hal!

On Tue, 25 Jun 2019 23:07:55 -0700
Hal Murray <hmurray at> wrote:

> You want something that reads to a small fraction of a degree.  I
> don't know of a great setup to recommend.  The standard CPU or disk
> temperature reading is usually only good to 1C.  That's great for
> monitoring CPU/disk temperature, but not good enough for making great
> plots.

I get very obvious correlations comparing the CPU temp, which is on the
back side of the PCB from the xtal, to the NTP frequency offset.

The RasPi CPU temp resolution in 0.1C increments

    # vcgencmd measure_temp

You can see all that here:

Very easy to see my central heat/air cycling.  About a 4C CPU temp
change cause about 500 uS clock offset.

If I use program to maintain the CPU at a constant temp then my
frequency offset gets very stable.

> Eric and Gary came from GPSD.  They think it is the solution to all
> problems.

It is!

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at  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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