SIMBAD references

We propose a statistical measure suitable for comparing the rotational stabilities of pulsars with one another and with terrestrial time scales. By a simple extension of notation long used in the clock community, we call the statistic σ_z(τ). Defined in terms of third-order polynomials fitted to sequences of measured time offsets, σ_z(τ) is sensitive to variations in the frequency drift rate of the clock or pulsar. We apply the new statistical formalism to real pulsar data and terrestrial time scales, and show that over the past 10 years these two kinds of data have comparable stabilities.