[time-nuts] ADEV vs. OADEV

Magnus Danielson magnus at rubidium.dyndns.org
Thu Jan 22 17:26:20 EST 2009

Hi Tom,

Tom Van Baak skrev:
> 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.

This at least explains the origin of the OADEV name. Many thanks.

If you look at the NIST paper that Bruce gave a link for, it makes very 
clear that the overlapping Allan deviation/variance should be used and 
that the original Allan deviation/variance should only be used "when 
necessary". The original form allows for some useful reductions in 
computation as a form of "quick" processing could be made with factor 2 
tau steps.

> See the tool page, which includes source code:
> http://www.leapsecond.com/tools/adev1.htm

I will look at it again, as I recall I have looked at it earlier.


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