Calculate sum for field in subreport

[Newposter]

I have a Report which includes two Subreports, linked by a one-to-many relationship of the Part Number field. In one Subreport, I have a field showing Annual Usage of an assembly. What I'd like to do is have a field summing all of the Annual Usages for the records in that Subreport that correspond to a Part Number. So for a part number used in 4 different assemblies, all with some annual usage, I'd like to display the sum of the 4 usages on my report.

When I try to use a text box with code =Sum([AnnualUsage]) it prompts me for a value when I open the report. If I leave it blank, nothing is shown for the sum. How do I code this box to reference the sum of each grouping of part numbers? Newposter
"Good judgment comes from experience. Experience comes from bad judgment."

 

[jonathonoss]

I would like to know the same. In addition, I would like to know how to identify if a subreport is 'null' for a particular record. 'Is null' and Isnull() and NZ() do NOT work for fields on a subreport. Any ideas?

Jon