I can't work the search function RE: StdDev

I was trying to search for one of the outstanding posts about Standard deviation and variance...
(I [img]/images/graemlins/heart.gif[/img] BruceZ)
Specifically how standard deviation is determined in relation to poker.
I know SD is sqrt(Var)
and to find variance (of a single play) we subtract the expected value from each possible outcome, square the differences, multiply the squares by their probabilities and sum.

How do we find the variance of all our play in terms of winrate i.e. BB/100?