kabbes
First intersubjective, then internalised
You don't want to EVER use a sumproduct, really. You want to use array formulae properly. Sumproduct, for example, should beWhat gets me, is they're always touted as sime holy grail, when people would be much better learning how to really work a sumproduct first.
{=SUM(IF(range1 = range2, range3 * range4, 0))}
It's a hell of a lot more powerful, because it allows you the full access of possible formulae rather than just summing the product if one value equals another.


bearing in mind I have mainly end user and limited experience of Access and that the Job Description states: