By this litlle post I'd like to thanks this forum and Jim of course.
It's not an easy way to make some App, but with the help and explanations i received ,
i managed to dev my first WF with some interesting features (at least, for me !) like BG, OS, Persistent to disk Storage and so on.
I made it for my own and put it in the Store, in case it may be interesting for some people...
I did not need any graph (even if i'll make some MoveBar ...), just some informations...
Maybe still some bug (like one i just find when updating only 1 Stock Code from Settings... Will work on it asap !)
So let me introduce you my Watch Face :
https://apps.garmin.com/fr-FR/apps/0ac97c3d-bbd5-4d12-a8f3-606e53691603
Thanks !