Add New Column to show Measurement Difference

I've seen several similar posts but these have not helped me. Thus if you have a moment would you please take a look?

1. What I want to do: Add a new column to a Matrix that shows the difference between two other columns

2. My Schema (in French but I've added English to help)

3. What I want it to look like:

Here's the current Matrix which has the "Question" as the Row, The "Campaign" as the columns, and the Measurement (see below for details)

4. The Measurement (this calculates the Quality):

R_CONFORME_SANS_NA =
DIVIDE
( CALCULATE(sum(F_QUALITE_REPONSE[R_CONFORME]), F_QUALITE_REPONSE[R_CONFORME_NA] <>1 ) ,
CALCULATE(COUNT(F_QUALITE_REPONSE[QUESTION_ID]),
F_QUALITE_REPONSE[R_CONFORME_NA] <>1 ))

5. What I want it to look like

This is an example of the new 3rd column that shows the "Delta" or "Difference" between the two columns

Issues:

I've tried creating a new measurement and referencing that but the SUM function I use expects to see a column in a table (and not a measurement).

Thank you kindly for your help on my first post to the Forum. I tried to make this as clear as possible I hope!

Grixelle