In image files:
Click on the ‘Scale’ field and choose ‘Set scale on drawing’ from drop down menu. Pick two points on the drawing that is opened and then a new window appears.
Enter the length you have marked on the drawing, click ΟΚ, and the scale appears on the drawing. Click the Update and close button to save the new scale. If you select ‘Reset scale’ from the drop-down menu, then the scale is set to its default value (1:1).