RowSourceLookup(RowSourceColumn [, tuple]) returns the row source column value for the current cell. RowSourceColumn is specified as an Identifier with the form [RowSource Name].[RowSource Column Name]. The return value type is the same as the row source column referenced.
Example:
RowSourceLookup([ComponentMetrics].[standardCost])
returns the value standard cost from the current cell's ComponentMetrics row source.