[time-nuts] σ vs s in ADEV

[Tom Van Baak]

> A number of outfits were measuring and spec’ing short term stability in the 1950’s and early 1960’s.

For "ADEV" in the 1950's -- follow the words in yellow [1]:

http://leapsecond.com/pdf/1953-Quartz-Greenwich.pdf

For "ADEV" in the 1930's -- I've seen similar treatment done by precision pendulum clock guys. Basically anyone that works with clocks knows to remove initial time offset and constant rate offset when determining the quality of the clock. What's left is the 2nd difference, which is the unexpected deviation in rate. I remember reading a pendulum clock paper from that era where they take the rms of these deviations and call it some kind figure of merit. It goes by other names now, like two-sample variance, sigma(tau), Allan deviation, etc.

/tvb

[1] The original, without OCR or highlight: http://adsabs.harvard.edu/full/1953MNRAS.113...67S