PLNAR now gives you the ability to measure floor to ceiling.
Make sure you have measure the perimeter of the room or at least one wall
Point the AR target at a wall segment and the "lift" button to the right of the main button will show up.
3. Tap and hold the "Lift" button which is the up arrow to the right of the main white button.
4. Drag the line to the edge of the wall and the ceiling.