The terms accuracy, stability, and precision are often used in describing an oscillator's quality. This slide illustrates the meanings of these terms with respect to a marksman and a frequency source. Accuracy is the extent to which a given measurement, or the average of a set of measurements for one sample, agrees with the definition of the quantity being measured. It is the degree of "correctness" of a quantity. Reproducibility is the ability of a single frequency standard to produce the same frequency, without adjustment, each time it is put into operation. From the user's point of view, once a frequency standard is calibrated, reproducibility confers the same advantages as accuracy. Stability describes the amount something changes as a function of parameters such as time, temperature, shock, and the like. Precision is the extent to which a given set of measurements of one sample agrees with the mean of the set.