Thanks again for your approach. It might be usefull for others.
However, I have no clue how but, I was able to do this without creating any union nor calculated field. Indeed, during my first days of learning and praticing with Tableau, I could make it "by accident".
The only thing I remember is that a played with Continous and Discret data.. :-/
Any oyher suggestions ?
Thank you Shin for your suggestion.
Smart idea but not convenient.
As soon as i find out how i have done it in the past, i will come back and leave a comment.
But i can guarantee you it was just a simple drag and drop and 2 or 3 clicks... not more.
In the meantime, if others have an idea, feel free to share =)
PS: here below, a screenshot of a PDF i have generated in the past, with my evolutive data + sparklines.
This is what i would like to reproduce