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 ¿ of the time intervals during which the measurements are made. The main advantage of this term is that it is independent of ¿. 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.