When Kyle is tracing the locations from which Sarah sent him IM's he sees that the 4 locations make a perfect square and deduces that the meeting location is at the dead center of that square. He plots the 2 diagonal lines and zooms in on their intersection, which is at the square's center. As he zooms in, the lines SHOULD have stayed as they were, perfectly perpendicular, but instead they skewed out to the corners of the computer screen destroying the perfect right angles.