Calibration: Make sure the room is well lit. The App needs to be able to see texture on the floor. If it is dark or an all white ground, it won't detect well. Turn on Flashlight (Auto) in settings to have the flashlight auto turn on.
Calibration: Make sure the area that you "calibrate" on is a flat surface.
Walk around a few seconds after calibration to let PLNAR "Discover" the area
Double check the distance to floor to make sure that PLNAR "Discovered" the floor correctly. THIS IS THE MOST IMPORTANT THING YOU CAN DO TO INSURE ACCURACY!!!!
Measuring: Try to stay within a 5-10 foot circle when setting the perimeter of the room using freeform mode. Use the guidelines if you can't see the corner.
The most accurate way to measure a perimeter is using RECTANGLE MODE - http://help.plnar.co/plnar-app-faqs/how-to-create-room-perimeters-using-rectangle-mode
Fine Tuning: After setting the perimeter, you can move closer to each point or line and place it perfectly.
Vertical: When establishing ceiling height, it is best to pick the segment that maps to the seam and stand away from the wall so you can see the entire wall.