sameperiodlastyear

Hi, I'm relatively new to Power Bi and for starting i wanted to do a tutorial. In there they ask you to calculate the total sales and the last year sales, for that they give you the formula:

• Total Sales = SUM(Sales[Revenue])
• LY Sales = CALCULATE([Total Sales],SAMEPERIODLASTYEAR('Date'[Date]))

but both give me the same result. in fact, i tried this

• Total Units = SUM(Sales[Units]) 
• LY Total Units = CALCULATE([Total Units],SAMEPERIODLASTYEAR('Date'[Date])

but this two also give me the same value( between this two, not with the firsts ones)

I'm afraid its a mess with the funtion CALCULATE or SAMEPERIODLASTYEAR, but i couldnt get any clue.

BTW, i tried also without result LY Sales = CALCULATE([Total Sales];SAMEPERIODLASTYEAR(DATEADD('Date'[Date];-1;YEAR )))

Any help would be apreciated, thanks