Creating Custom Calculated Members and Sets in OLAP PivotTables
If you are using PivotTables against an OLAP data source you may find it useful to be able to create your own custom, calculated measures and sets. These calculations are client-side meaning they exist inside Excel and you don't have to change the server-side OLAP cube.
Excel does not enable you to do this using the user interface, however, you can do this via the API.
Allan Folting (our PivotTable expert) has published a post showing how to do this using VBA over in the team's blog.