Using PowerPivot in Excel 2013 - Business Intelligence in Microsoft SharePoint 2013 - page 117

PowerPivot evaluates the DAX expression for each row of the FactInternetSales table and popu-
lates the FactInternetSales [Margin] column with the result, as shown in Figure 4-28.
FIGURE 4-28 A simple DAX calculation.
Here's a slightly more complex DAX formula:
=SUMX(RELATEDTABLE(FactSales),FactSales[SalesAmount])
Here, the DAX expression calculates a value for each row by scanning the rows in the FactSales
table for the current row (from the DimProduct table). In other words, this DAX formula filters the
FactSales table that corresponds to the product of the current row and aggregates the SalesAmount
value, as shown in Figure 4-29.
FIGURE 4-29 Applying a more complex DAX formula.