[time-nuts] σ vs s in ADEV

Tom Van Baak tvb at LeapSecond.com
Mon Jan 9 18:52:56 EST 2017

Hi Jeremy,

> the 5360A "Computing Pig"
> I've never figured out the difference.

See the top of page 11 of http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1971-11.pdf where it says:

    "Fractional frequency deviation is the term used to describe the frequency
    instabilities of a source in the time domain. It has been shown [4] [5] that a
    meaningful quantitative measure of fractional frequency deviation is given
    by the Allan variance:"
    4. D. W. Allan, 'Statistics of Atomic Frequency Stan dards,' IEEE Proceedings, Vol. 54, No. 2, 1966.
    5. NBS Technical Note 394, 'Characterization of Fre quency Stability.' 

So that's the same as the definition given, for example, here:

There is one source of confusion: ADEV (Allan deviation) is the square root of AVAR (Allan variance). We almost always calculate and plot AVAR. The other confusion is Allan (it's not Allen).


The 5360A is still a favorite of us old-tyme collectors. Lots of information on the old thread (you're in it):

"HP 5360A History?"

The 5360A source code to the ADEV program is here:


----- Original Message ----- 
From: "Jeremy Nichols" <jn6wfo at gmail.com>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Monday, January 09, 2017 2:09 PM
Subject: Re: [time-nuts] σ vs s in ADEV

In the late 1960s, Hewlett-Packard engineers worked up a program to have
the 5360A "Computing Pig" (so-called from its weight, 55 pounds without
plug-ins) compute a "fractional frequency standard deviation." It appears
to be similar to the Allen Deviation; I've never figured out the difference
and would appreciate hearing from someone with stronger math skills who can
explain the two.


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