Time Standards and Statistics

Time standards are usually characterized by terms such as "stability," "accuracy," and "precision," without general agreement as to what these terms mean. As a logical substitute to these terms, "relative instability,' "reliability," and "unreproducibility" are offered. Relative instability is the standard deviation of several measurements of the frequency ratio of any two clocks, divided by the square soot of the mean μ of the time intervals during which the measurements are made. The main advantage of this term is that it is independent of μ. Reliability is identified with the number r of clocks being intercompared and is required to be ≥ 3. Unreproducibilify is the standard deviation from unity of the frequency ratios of all pairs of the r clocks.