Although I managed to hack a solution, I personally think that it wouldn't be worth the effort, i.e. it would have been quicker and easier to manually add reference lines.
Not knowing the logic for calculating the % of Goods for each % of Profit, I just used a fitted trend line regression equation, but this would change if the data changes. I don't see an easy way to come up with a universal formula for this - it sounds like something that requires a PHD in Statistics.
In addition, the hack requires a bunch of table calculations, some tricky formatting, etc.. In other words, it is too much work.
tableau_labeleg_mod.twbx 61.0 KB