[time-nuts] ADEV vs. OADEV

Tom Van Baak tvb at LeapSecond.com
Thu Jan 22 10:01:10 EST 2009

Hi Magnus,

I've never seen it in print either but I coined the name when I wrote
my ADEV tools. I've found a profound difference in the overlapping
form of ADEV in many cases and so I use it a lot now -- especially
when analyzing the effect of tides on precision pendulum clocks, or
other periodic effects, such as cycling A/C or diurnal effects.

However almost every technical paper in the past few decades uses
the plain old textbook non-overlapping back-to-back ADEV so my
software tools call the traditional calculation "ADEV" and I call the
overlapped version "OADEV".

An alternative was to use words "ADEV(normal)", ADEV(overlapped)"
and "ADEV(modified)" but I chose the shorter ADEV, OADEV, and
MDEV instead. "ADEV" and "MDEV" are already standard, and so
"OADEV" seemed to fit. So far no one has been confused, but I can
see your point.

See the tool page, which includes source code:


----- Original Message ----- 
From: "Magnus Danielson" <magnus at rubidium.dyndns.org>
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Sent: Wednesday, January 21, 2009 12:32 AM
Subject: [time-nuts] ADEV vs. OADEV


I have been quite surprised to see the abbreviation OADEV appear. I
assume that this means Overlapped Allan Deviation, but this is confusing
since the Allan Deviation estimates already is overlapping. However, I
have seen that some use a non-overlapping estimator, but this type of
estimator has an unwanted filtering effect and should not be used.

If a distinction between these ADEV estimators should be used, then the
standard (overlapping) estimator should continue to be called ADEV and
the non-overlapping (back-to-back) could be called NOADEV ór whatever...

I have done a fair amount of digging around many sources around ADEV and
friends so I think I got it right.

Unless someone can give a meaningful explanation and I really expect a
good article detailing the difference and benefits...


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