Standard deviation () and root mean square deviation (s) are measures of dispersion in a data set. is calculated as the positive square root of the average of the squared deviations from the mean, while s is the positive square root of the average of the squared deviations from an arbitrary value A. It is shown that s2 = 2 + (x - A)2, where x is the mean and d is the difference between x and A. This indicates that will always be less than or equal to s, and reaches its minimum value when A equals x. Therefore, standard deviation provides the smallest possible value of root mean square deviation.