Your drawing is highlighted in blue whenever you try to take a measurement.
This happens because the document contains at least one viewport which defines the scale and units of measurement.
You can remove the unwanted viewport by following the steps listed below:
- Open the Measurements (Alt+U) panel and expand the Viewports section.
- Under Viewports, the list on the right will show the viewports currently on the page. Most likely, there will be multiple viewports with the names “Untitled.”
- Select Clear All to remove all of the viewports on that page.
Once this is done, you can change the scale of the drawing within the Scale section of the Measurement panel, or set a new scale by calibrating the drawing.
If you already have measurements on the drawing, click the Recalculate button in the Scale section of the Measurements panel. This will recalculate the measurements according to the scale and units that are defined for the page.