Incredible oneliner

This oneliner is incredibly useful:

gawk '{avg=avg+$2; sd2=sd2+($2*$2)} END{avg=avg/NR;sd2=sd2/NR; print avg" "sqrt(sd2-avg*avg)}'

It calculates the average and the standard deviation of a column in a set.

I know it may sound trivial, but I didn't know that you can calculate the sd by adding the square of each term (I always calculate it by adding the square of the difference with the average).