Rotate UCS and apply this routine to get BBox, then extract only width (red line)...

Thank you Ribarm!

Works !

But I was hoping for a mathematical solution. . .

Because this routine does a number of very spectacular things,

while I'm looking for something that can't be seen,

that makes calculations "in secret" ...

But I realize that it is a very complicated thing!

I have to try to do something only for lines, circles and arcs...

It shouldn't be hard...