% Variation Over Years - DAX synthax issues

Hi the community, 

I'm making progress with PBI, specially in YOY analysis, but i'm still stuck with beginner issues... 

So here is my problem : 

I was looking to calculate variation quantity YOY, like in this example : 

I created a calandar table to help me in YOY comparaison, like it seems to be recommended. 

I did those two calculation for the while : 

- Quantity LY = CALCULATE(SUM("Sheet 1" ^[Order Quantity]), SAMEPERIODLASTYEAR ("Calendar Table" [Date])

- Quantity Diff Between CY LY = SUM("sheet 1" [Order Quantity] - [Quantity LY]

Now i'm trying go get this Difference in Variation %  : 

I tried this : 

% Variation CY LY =
VAR _currentyear = SUM('Scrap Projection'[Order Quantity])
VAR _LastYear = [Quantity LY]
RETURN
_currentyear - _LastYear / _currentyear

But my result had no sense... 

I'm sure i'm missing something simple... Anyone can advise me ? 

Thanks in advance 🙂