I don't know how do you want to calculate that change, but say its the change between the price of the current line and the previous line. The, the expression would look like
([Price] - above([Price])) / above([Price])
Of course, it depends on your chart pivoted positions and so.
Hope that helps
You have different solutions for that.
One is sort dimensions so they always bi in that order needed for the formula to work. Use the Sort tab in the chart properties for that.
Another is to create conditions
or something similar, but the more complex your expressions are, the longer it takes to calculate the chart.
if([Seller] = above([Seller]), ([Price] - above([Price])) / above([Price]))