Oh, my! It works! Thank you guys so so much!
TIG you are a Ruby wizard! Thank you for your patience

So, here is my final result:

Thanks for advice, TIG, but I already tried it... It's too hard code for my low programming skill.
Could you answer me:
Where can I find sketchup dimension tool code for try to edit it? (Is it possible?)
Or how could I solve my problem another way (maybe by replacing text in existing dimensions)?

My current "frankenstein"-code :

require 'sketchup.rb'
SKETCHUP_CONSOLE.show
UI.menu("Plugins").add_item("DimPlugin") {addim}

def addim
entities = Sketchup.active_model.entities
dim = entities.add_dimension_linear [50, 10, 0], [100, 10, 0], [0, 20, 0]
dims = Sketchup.active_model.entities.grep(Sketchup;;Dimension)
i = 0
dims.each do |d|
i+=1
d.text = "D#{i}"
end
end

Thanks again

Thank you! It works much better!

But I still need a way to pick two dimension's points.
Or another decision (if it easier):
I could make dimensions by default Sketchup tool, but then I would to replace all of them by my plugin.

Thank you guys for replying
So, after titanic labour I have produced this:

require 'sketchup.rb'
SKETCHUP_CONSOLE.show
UI.menu("Plugins").add_item("DimPlugin") {addim}
def addim
  entities = Sketchup.active_model.entities
  dim = entities.add_dimension_linear [50, 10, 0], [100, 10, 0], [0, 20, 0]
 dim.text = "D1"
end

And questions:

1. How can I choose points for a new dimension (like basic sketchup tool "Dimension" does)?
2. How can I create multiple dimensions (D1, D2, D3... etc)?

Thanks again...

Hi all.

I'm not a Ruby programmer and having a headache with one simple question:
Is it possible to create a plugin for making numbers of dimensions instead measurements?
For examle: D1, D2, D3... etc

Asking for help.
Thanks in advance