Editing Allan variance (section)

===Measurement instrument estimator bias===
Traditional instruments provided only the measurement of single events or event pairs. The introduction of the improved statistical tool of overlapping measurements by J. J. Snyder<ref name=Snyder1981/> allowed much improved resolution in frequency readouts, breaking the traditional digits/time-base balance. While such methods is useful for their intended purpose, using such smoothed measurements for Allan variance calculations would give a false impression of high resolution,<ref name="Rubiola2005">{{Cite journal|url=http://www.femto-st.fr/~rubiola/pdf-articles/journal/2005rsi-hi-res-freq-counters.pdf |doi=10.1063/1.1898203 |title=On the measurement of frequency and of its sample variance with high-resolution counters |year=2005 |last1=Rubiola |first1=Enrico |journal=Review of Scientific Instruments |volume=76 |issue=5 |pages=054703–054703–6 |arxiv=physics/0411227 |bibcode=2005RScI...76e4703R |s2cid=119062268 |url-status=dead |archive-url=https://web.archive.org/web/20110720220221/http://www.femto-st.fr/~rubiola/pdf-articles/journal/2005rsi-hi-res-freq-counters.pdf |archive-date=20 July 2011 }}</ref><ref name=Rubiola2005ifcs>Rubiola, Enrico: [http://www.femto-st.fr/~rubiola/pdf-articles/conference/2005-ifcs-counters.pdf ''On the measurement of frequency and of its sample variance with high-resolution counters''] {{webarchive |url=https://web.archive.org/web/20110720220233/http://www.femto-st.fr/~rubiola/pdf-articles/conference/2005-ifcs-counters.pdf |date=20 July 2011 }}, Proc. Joint IEEE International Frequency Control Symposium and Precise Time and Time Interval Systems and Applications Meeting pp. 46–49, Vancouver, Canada, 29–31 August 2005.</ref><ref name=Rubiola2008cntpres>Rubiola, Enrico: [http://www.femto-st.fr/~rubiola/pdf-slides/2008T-femto-counters.pdf ''High-resolution frequency counters (extended version, 53 slides)''] {{webarchive |url=https://web.archive.org/web/20110720220251/http://www.femto-st.fr/~rubiola/pdf-slides/2008T-femto-counters.pdf |date=20 July 2011 }}, seminar given at the FEMTO-ST Institute, at the Université Henri Poincaré, and at the Jet Propulsion Laboratory, NASA-Caltech.</ref> but for longer ''τ'' the effect is gradually removed, and the lower-''τ'' region of the measurement has biased values. This bias is providing lower values than it should, so it is an overoptimistic (assuming that low numbers is what one wishes) bias, reducing the usability of the measurement rather than improving it. Such smart algorithms can usually be disabled or otherwise circumvented by using time-stamp mode, which is much preferred if available.