We evaluate with simulated data a new type of sample variance for the characterization of frequency stability . The new statistic ( referred to as TOTALVAR and its square root TOTALDEV ) is a better predictor of long - term frequency variations than the present sample Allan deviation . The statistical model uses the assumption that a time series of phase or frequency differences is wrapped ( periodic ) with overall frequency difference removed . We find that the variability at long averaging times is reduced considerably for the five models of power - law noise commonly encountered with frequency standards and oscillators .