Your drawing is highlighted in blue whenever you try to take a measurement.
This happens because the document contains at least one pre-existing viewport, which defines the scale and units of measurement. If the entire page turns blue, that means there are multiple overlapping viewports which should be removed.
You can remove the unwanted viewports by following the steps listed below:
- Open the Measurements panel and expand the Viewports section.
- Click the Clear Viewports button to remove all viewports from the page, or the entire document.