Paneling tools -> ptPanel3DCustomVariable -> MeanSurfaces...how?

Hello!

I’m getting into paneling tools and have problem with the option MeanSurfaces in ptPanel3DCustomVariable.
I get weird or no results but I think it has to do with the last steps in the command where I’m supposed to:
Select objects to define the 3D bounding space” I’ve tried making a box to define this but I’m not sure that’s the right way. Anyone who can guide me a bit on this one?