**Significant Figure:**

Digit: Any one of the ten numerals, including zero.

Significant figure: A digit which denotes the amount of the quantity in the place in which it stands e. g. 1.3280 and 1.0032 – zero is significant, whereas 0.0025 – zero is not significant but only to locate the decimal point.

**Standard Deviation:**

It is the square root of the mean of the sum of the squares of the differences between the values and the mean of those values and is of particular value in connection with the normal distribution.

Suppose series of ‘n’ observations arranged in ascending order of magnitude like X_{1}, X_{2}, X_{3}, X_{4}, X_{5}, X_{6}……….Xn

The mean of this value is

X = (X_{1}, X_{2}, X_{3}, X_{4,} X_{5}, X_{6}……….Xn) / n

Standard deviation (s) = square roof of: {(X_{1}-X)^{2} + (X_{2}-X)^{2}…….(Xn-X)^{2 }} / (n-1)

Relative standard deviation (R.S.D.) = standard deviation / Mean