Hello. I'm using this formula in Dax powerpivot Sum of Revenue YoY%:=if( NOT(ISBLANK([Sum of Revenue])), DIVIDE(([Sum of Revenue]-[Sum of Revenue PreviousYear]),[Sum of Revenue PreviousYear]))

Per the book, it says if sum of revenue is empty, it returns a blank. Where is that specficied? Is there a way to walk through formula like in regular excel? It's sort of hard to keep track of these monstrosities.