It took me a bit of fiddling around to understand how to add measures and KPIs to PowerPivot models with the SQL Server 2012 PowerPivot update. In particular, the newly-added Calculation area wasn’t intuitive for me to work with.
To that end, I recorded a short screencast of the steps I use in both Excel 2010 and also in Visual Studio 2012. In the latter I am using an add-in from CodePlex called the ‘DAX Editor for SQL Server.’
Another helpful resource for me in this process was this MSDN article which contrasts ‘Calculated Columns’ with ‘Measures’ in PowerPivot.