Thank you Thomann Harley Benton.
I just put this ruler on the neck and look for space. I put a light and colored background. I have a set of measuring strips, but eye observation works.
You can see the trussroad action in real time.
This prevents any damage or unintended settings.
The best compromise if neck curve setting can obtained easily. In my case, after exploring with completely flat neck, I went back to a setting with a little space, less than 0.40 mm in the middle of the neck, so I can dig with a pick on lower strings, and play with fingers.
In summary I could choose the curve so it does not “buzz” where I play the way I play :)
Great tool. Easy and essential at some point in a guitar journey.