I have the following array formula, works correctly for me in cases where
both input values are nonblank, but i don't get the result i need if one or
the other is blank.  Here's the formula:
{=SUM((data!A11:A61-AVERAGE(data!A11:A61))*(data!B11:B61-AVERAGE(data!B11:B61)))}
[Actually if you are interested, it is the crossproduct term, the numerator
of the formula given the help file for the Excel SLOPE function].

What i want the formula to do is skip any row in which a value in range
A11:A61 OR B11:B61 is blank, and continue to return the crossproduct sum for
the rest of the rows where both values are nonblank.

Any array formula experts out there know a way to do that using array
formulas?

Thanks, tom