The reason for doing so is that, in many situations, it is easier to calculate the moments in the first instance, about an arbitrary origin. They are then transformed to the meanmoments using the relationships that I am now going to convey to you. The equations are:
m1 = 0 m2 = m'2 − ( m'1 ) ; 2
m 3 = m'3 −3 m'2 m'1 +2 ( m'1 ) , and 3
m 4 = m'4 − 4 m'3 m'1 + 6m'2 ( m'1 ) − 3 ( m'1 ) 2
4