Bruce Griffiths skrev: > Ulrich. Magnus > > Perhaps the situation is best summarised in /NIST special Publication > 1065/ (can be downloaded as 2220.pdf > <http://tf.nist.gov/timefreq/general/pdf/2220.pdf> from NIST) wherein it > is stated that ADEV, AVAR are often taken to mean the overlapped form of > the Allan deviation at least in the US.
This is an excellent contribution to the discussion as it details the "Original Allan variance" and "Overlapping Allan variance" and also has a special information box detailing that AVAR and ADEV used mainly (notice standards and much of the reference material) for the overlapping. It also shows the inability for the 2-sample variance (Original Allan variance) to create smooth and good curves. That the 2-sample variance existed and was the basis for Allan variance was know, but the overlapping formulation of the established AVAR and ADEV terms estimators is motivated and accepted for its improved precission was also known to me indirectly, in the sense that I saw they where not directly equivalent but saying the same thing, then I forgot about it until this mysterious OADEV/OAVAR came up recently. There is however a huge difference between the 2-sample variance being the original Allan variance and being AVAR. Here I tend to rely on standards set by IEEE and ITU-T as they establish a defined relationship and I suspect some wisedom was applied in the process. Which estimator is we best serviced by to get defined as AVAR? They chose the overlapping one and it has also been the most used in theoretical analysis to the best of my knowledge. The plots given in the NIST SP 1065 figure 8 is very descriptive on the difference. In the end, I think we must realize that there is a distinction between the 2 sigma (tau) y and AVAR(tau) The former is the Original Allan Variance where as the later is the Overlapping Allan Variance. It is easy to confuse the two. Maybe this is the fundamental problem and not the definitions themselfs. Cheers, Magnus _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.