- is just the minus sign. The magic is that it forces conversion of an array
of true/false values to numbers, actually -1/0. The second minus sign just
restores the proper sign. So --true is 1; --false is 0. Once you've turned
your arrays from true/false to 1/0, the sumproduct can work as it normally
does on arrays of numbers.

"Mike" wrote:

I have a formula that looks as follows:

=IF(AND(H24="NEX",$C24="Operations",U$15="Yes"),SU MPRODUCT(--($D$17:$D$228=D24),--($H$17:$H$228="EX"),$T$17:$T$228)/SUMPRODUCT(--($D$17:$D$225=D24),--($H$17:$H$225="NEX")),"")

What is the prupose of the -- in the formula?