Best practices question

Gary E. Miller gem at
Wed Jun 26 20:35:30 UTC 2019

Yo Paul!

On Wed, 26 Jun 2019 13:14:36 -0700
Paul Theodoropoulos <paul at> wrote:

> I think maybe I'm  hitting a bug or I'm just not understanding
> (usually the latter), as it doesn't seem possible:

No one totally understands this.

> jitter fluctuating between 400 parts per trillion and 800 ppt?? From
> a Raspberry Pi running at 1.4Ghz?

Here is mine:

My Standard Deviation is 48.504 ppb (10e-9)

Your Standard Deviation is 82.8 10e-12)

So about 500x better then mine.

But my numbers are over 24 hours, not one.  So the diurnal ambient changes
are in mine, not yours.

I get a lot better when I put the RasPi in a temp chamber and control
the CPU temp.  But not 500x better.

> That said, I switched to min/maxpoll 1 for PPS, and saw a
> corresponding change - so Time jitter appears to be inversely
> correlated to Frequency jitter - less frequency jitter, more time
> jitter, and vice-versa. This is all fascinating.

This sort of relates to a current discussion on time-nuts.  They
are discussing the relative merits of a PLL vs an FLL.  Similar effect

The shorter poll keeps the time closer to the PPS, but magnifies the

"And if you go chasing rabbits, And you know you're going to fall..."

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
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 851 bytes
Desc: OpenPGP digital signature
URL: <>

More information about the users mailing list