First you make a database connection to the excel spreadsheet and configures which data you want to show.
Then you add the results to your mindmap.
To use the AutoCalc, you select a topic and add a property (or as many as you would like) of the type Calculated and you select the propertyname of the spreadsheet to complete the calculation.
In the image below you can see the result.
Of course you can always embed the spreadsheet itself and use it's rich calculation features, in stead of the limited AutoCalc...