Many users use in-cell formulas to calculate values, on which they perform their analysis.  Prism works great with in-cell formulas because it generally references the value of the cell, not the formula that creates it.

However, you need to pay attention to TYPE of value your formula returns.  For example, if you use the formula =IF(A2="INCOME","0",D2) to calculate the value of a cell, you will get the STRING value zero if the value of A2 is the string value INCOME.  This is what using double quotes mean in Excel.

If you want the TYPE of the cell to be numeric, you must alter the formula a bit: =IF(A2="INCOME",0,D2).

This directly affect the way Prism identify field types.  See http://community.sisense.com/forums/t/58.aspx