I don't think there's any such thing. I guess it depends on your flying experience. I did a demo some time ago for the local Rotary Club in a pub's conference room and din't have any issues. Also the floor was covered with a brightly patterned carpet which helped the vertical stability. Follow the steps below to use Vision Positioning:
1. Toggle the flight mode switch to P-mode.
2. Place the aircraft on a flat surface. Note that the Vision Positioning system cannot work properly on surfaces without clear pattern variations.
3. Turn on the aircraft. The aircraft status indicator will flash green two times, which indicates the Vision
Positioning system is ready. Gently push the throttle up to lift off and the aircraft will hover in place.
Make sure you have plenty of clear space around the takeoff point so you have time to correct any sideways movement.
Practice outside first! Read the manual, page 15.