Tx for your reply.
The 1st solution don't work, if I work with a 2D sketch
OK, R² is a sub manifold, when embedded in R³, but R² has a manifold structure too - ie an intrinsec structure.
So, I should have not to embed the 2D sketch into the whole space, to define some orientation.
Otherwise, I found a third solution on the forum
which works, but it's really funny to see that SW don't define any orientatiobn of a plane, when created, and force to such recipe.
Unfortunately, this is not the only really serious math mistake I found with this program.!!!
It's really serious that such mistakes are still living in a program, after n spread versions, n being greater than 20 or 30 !!!!
More and more funny : impossible to use Tools->Sketch tools-> modify, when an external reference is defined in the sketch.
And of course, to be completed, SW says nicely that it's impossible, but forgets to list what could be defined as external references in the sketch.
How can a enginers team work with such lame program ?
You can list your relations and then choose external references to see them. You have the choice to delete them all.
I agree completely that the user should be able to choose which normal to use for a plane, but I have not had any luck convincing SolidWorks to give us that ability. They came up with another workaround in a recent version, probably 2012, but I am still stuck on 2010 and have already forgotten what the workaround was.