3d distance in a space point

[[Ra...]]

What does the 3d distance in space point mean compared to nominal zero, as does the sign attached to it mean something?

[[No...]]

It's the spatial distance (3D vector) of the actual point from the nominal point [square root of (dX^2+dY^2+dZ^2)]
The sign probably indicates whether the vector points to the surface or away from it, in other words, if the actual point is inside or outside of the nominal surface. But don't ask me which is which. I never needed this, but I'd say + points to the outside and - to the inside.