You can define named ranges for A1:A10, B1:B10 and C1:C10, using names
which are meaningful to you. You can also use names for the factors D1,
D2 etc. Then the formula will make more sense when you come to edit it
in the future. So, you might have something like:

=SUM(IF((names="ABC")*(parts="DEF"),cost,0))*facto r1

Hope this helps.

Pete