When I chose just one of the selections (I have been using "Product" no" = "or other signs) it only sums the values were there is only "Product" . the equation wont sum if there are other selections included.
A screenshot of your current sheet would help to understand what your're trying to achieve and what your data actually looks like.
this is what the source sheet looks like- where it has Tech Skill I would like to be able to select one Skill and Sum in the Month by that skill. So if i choose CP SME it would add 145 +60 (which are a Sum(Children)) field