Grids on tabular cubes
When accessing a tabular data source there may be some differences to multidimensional cubes.
You can define new measures in the cube on the fly.
To do this select the Measures dimension in the report designer, and drag an attribute from the "Available hierarchies" into the "Selections" area to the right of the normal measures list.
Once it has been added you can chose the aggregation type, Sum/Average/Min/Max for numeric attributes, Counts for other types.