Pair's premise is simple: open the app on your iPhone or iPad, aim its camera to the room, select a furniture model, and drag it onto the screen. Unlike other apps, Pair let's you walk around the room while keeping the furniture in place. This lets you intuitively understand a layout as it would be seen and used.
Of course, as with any seamless technology, it's easy to miss the complex systems working behind the scenes. However, Pair's complex algorithms didn't get their start at a software or architecture company, but rather at a U.S. Air Force base in Guam.