well the formula is √ { [∑(y-y')2]/(n-1)}
where y are the elements
y' is the mean
n= number of elements
manual method:
i'll use an example...
example: find mean and s.d. of 2, 3, 6, 10
mean = (2+3+6+9)/4 = 5
s.d.
calculate ∑(y-y')2
= (2-5)2 + (3-5)2 + (6-5)2 + (9-5)2
= 9 + 4 + 1 + 16...