Line Chart displaying two seperate time periods

[#1]

I am trying to create a line chart that displays sales data from a year that I select and would like it to also show me the same data from the previous year, and have it all broken down by months. Would love it if someone could help me on this, thanks in advance.

[#2]

You will need two expressions ... (samples)

sum( {$<Year = {$(=Only(Year))}>} Sales )
sum( {$<Year = {$(=Only(Year)-1)}>} Sales )

The first calculates the Sales for the selected Year and the second the same for the year before that.

You use the Month as a dimension.