Calculate percentage out of total

I want to build a stacked chart per month and segment (IND, AUT, ADP...). My stacked chart should show how much net sales products less than five years old make out of the total net sales within each segment. I have created a user dimension with two members; Less than 5Y and Total.

Could one please help with the syntax for this calculation? I guess I have to create a measure calculation and I tried this syntax which does not give me the right answer: sum(0, 0, m1) / sum(all, 0, m1)

My data sheet behind the chart showing the user dimension: