Your post requires some more inputs from your side to get the solutions from forum. Use the Sample Database, Mock up the a report with your question related data then explain clearly what kind of output you are expecting.
I am using Sample Database to explain here.
We have to define Addressing & Partitions perfectly.
2) Drag Sales on to Text, Right click, click on "Add Table Calculation",
3) Now we get the Result, Difference of Sales for Every Product from previous Year.
I hope the above approach will help you.