Define Standard Deviation. Write its two demerits

"The standard deviation is the square root of the arithmetic mean of the squares of all deviation. Deviations are measured from arithmetic mean of the items”.
(i) Difficult—The process of squaring the deviations and then to find the value of its square root is a time consuming affair. It is quite difficult too.
(ii) More important to extreme values—In calcu-lation of Standard deviation un-due importance is given to marginal values.