No problem with demand i don't take it to heart. I have a vertical and horizontal 360' laser level. I set up the laser took the level (height) from top of the flight and measured the distance from bottom of the flight till the lazer line as vertical as possible with a help of long bubble level. FFL to FFL 2640 wow ok i see why it is so important... I counted in laminate flooring but didn't count in the carpet and underlay from upstairs.