using ISBLANK

I've attached a spreadsheet which is to become a template for multiple reports.

I've tried to generate a graph using the table illustrated in the attached file, but am having difficulty.

Some of the tables will have empty cells. In my reports, an empty cell must not be counted as a zero. But if the empty cell becomes part of a formula using ISBLANK or ISNUMBER, the result is #VALUE!


Any advice?

Thanks.