When measuring an object, the measurement tools for 2D content snap the resulting markup to that object. Snapping is especially important for measurements, as the snap points determine the measurements displayed. Snaps are enabled by default.

Snaps display as small red circles
To disable snapping measurements to 2D objects
Repeat these steps to re-enable snapping measurements to 2D objects.
Repeat this step to re-enable snapping measurements to objects.