Go to the TI site find the Atomic Learning tutorials on the BA II there is one on stats and regression. The calc will give you the std Dev just square that.
The keys are something like, 2nd, data,
Then input your data as X1 hit enter skip Y1, then second input is X2 then hit enter, keep going until you have all of the or your data in.
Then hit 2nd, stat, toggle through and it will give you the mean and the SD.