I have 3 datasources and all three have a "Manufacturer" column. The measure "=# Number of records" show the aggregate number of that column (Manufacturer) across all 3 data sources.
I am looking for a way to limit the number of records (or a duplicate of that) to show me the number of records in "Manufacturer" column on a certain data source/dimension.
I assume you are taking a union of all of the data sources. If so, then try creating a calculated field [Number of Records in DataSource1]
IF [Table Name] = "DataSource1" THEN 1 ELSE 0 END