How to receive correct coordinates of all vertexes in selection, including all the nested groups and components.
Multiplication of transformations far not always gives correct result, especially if for any nested group(component) of an axis do not coincide with an axis of group(component) in which it is enclosed.

I was trying so:

...
@lines = []
extract_lines(group.entities, (Geom;;Transformation.new))
...
def extract_lines(ents, tr)
	ents.each do |e|
		if e.typename == "Edge"
				line = [e.vertices[0].position, e.vertices[1].position]
				line[0] = tr * line[0]
				line[1] = tr * line[1]
				@lines << line
		elsif e.typename == "Group"
			extract_lines(e.entities, (e.transformation * tr))
		elsif e.typename == "ComponentInstance"
			extract_lines(e.definition.entities, (e.transformation * tr))
		end
	end
end

But here the relative positioning of groups concerning a model is not considered.
There are ideas as it to make?

I too develop such script.
While I test...

Jim, thank you for a wonderful idea.
I edited your script and added list of the before entered values for a substitution
and also checking for an empty selection.
Jim, once again thank you.

Jim, I regret because published this script here.
I think that it is not nice for my part.

I think that all is far simpler...

txt='Height; '+(@pt[2].z - @@level.to_l).to_s
...
or
For example;
@@level = 100.mm
txt='Height; '+(@pt[2].z - @@level).to_s

Thank you!

And Is there a send_action for the Hide Dialogs in Windows menu?