@arpenteur ,
I looked at your drawing, I agree that should fix it up. I used the commands Edit drawing settings in the Settings tab of the prospector, and set the units to Meters in there. I also typed in UNITS and set the units to Meters in that location. Finally I suggest using the INSUNITS to set the controls for the units for the conversion/ scaling when importing drawings. Other than doing that on the beginning of everything, the next iteration should be much better now that those things are set up. I think your post is the solution, that others would use to solve their issue if they had the same issue.
This article has peripheral information that might have helped as well.
Objects are scaled when inserted into a drawing in AutoCAD
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Copper Chadwick
Designated Support Specialist