Using an array formula (once entered, hit cntrl+shift+Enter in th

formula field), use the following formula where A1:A9 is you

range/array of positive and negative numbers:

=STDEV(IF(A1:A9<0,A1:A9))

(which will look like {=STDEV(IF(A1:A9<0,A1:A9))} once entered a

mentioned above)

To