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Skewness. When calculating where the Screen is that you're presenting from, Upoint uses 3D marker lines that pass through the corners of the Screen, and assumes the Screen has horizontal and vertical sides. Mathematically, in a perfect world, two lines in 3D can only be connected by exactly one vertical line. In practice, however, measurements as well as a user's aim are never perfect. The Skewness Tolerance tells Upoint how much horizontal distance is allowed between the marking lines and the upper and lower corners of acceptable rectangles that it finds as possible solutions to the whereabouts of the Screen.