@Seatechfrance said:

Is it possible to set the model's scale value using an automatic text command?

Yes, you can use a label anchored to a viewport. In Shape Style you can edit the leader color to make it transparent.

There are a number of scrapbook items that already have this sort of thing set up. Bring in the Scrapbook item and drop it on the viewport. Then move it off leaving the leaders anchored to the model.