This is a common situation:  Don’t show me what my total sales figures were month after month, show me something that describes something important to my business.  ie, Sales Growth

Chris Webb, who runs a wildly popular MSFT blog in addition to being an in demand independent consultant, wrote an article on Previous Period Growth using Pentaho.  Mondrian (Pentaho Analysis Server) uses MDX, a powerful expressive multidimensional query language which Chris is one of the leading experts on its practical use and applications.

Chris outlines how to build a “custom” calculated measure that displays the Sales Previous Period Growth:

All you need is the zero install pentaho demo installation to run through his tech tip, available at http://www.pentaho.org/download/latest.php

Remember, this isn’t trivial (ie, writing MDX fragments) but it’s VERY VERY powerful.  Check out the Mondrian MDX reference here for some of the powerful analytic calculations available.  Remember, once you’ve got your MDX member working properly HIDE that complexity from your users by adding it to the Mondrian OLAP schema definition.