OLAP Tools convert to formulas adds sums and average to new measure in spreadsheet, but not in Data Model - how does this work?

[BaldAccountant]

I am new to using cubevalues with powerpivot. I made a new pivot table with averages and sums that are not measures in my datamodel in power pivot and when I used OLAP tools to convert the table it created a new measure in the spreadsheet that I can use in Cubevalue formulas, but it is not a measure in my datamodel. I don't like using formulas that I don't understand how they were created. How does this work? Is there a way I can create one of these measures that are useable in cubevalues in excel but are not in my datamodel.