waterfall chart logic

Hello, I am not quite sure how to phrase my question so I apologize in advance, I have a data-set which is fairly standard. We are evaluating the rental rate for each given period based on a DAX pattern in wich I use the typical cumulative total pattern (in reverse) very succesfully in getting my bar chart info which shows the declining revenue each month. The issue I am having is when I try to use show the to-go revenue for a given project, I can create a waterfall chart that shows this very easily but I want to just show this as a line in the bar chart and I cannot figure out how to to this. I assume that since the waterfall chart does this very calulation in just a few seconds that I have all of the required data but again I am stumped. I have spent approx 30 hours messing with this and I am giving up and asking for help.

The question is where can I get to the logic that builds the waterfall chart or is there a tutorial on custom waterfall charts the value I am after is the incrmental period to date total as well as the total at the end of the waterfall chart.

thank you,

josh