I have used (Current Year Sale - Last Year Sale)/Current Year Sale to give you a view that you want to see.
Hope the file attached helps.
11_10_12_TestV1.qvw 134.8 K
Thanks fr the helpful answer, but I had managed to solve it as it was required.
I had used" (sum(sales)-above(sum(sales)))/above(sum(sales)" and few design settings on graph.
This is providing me the required graph showing the percentage decrement and increment.( both + and -ve values plotted.)