Due to the quantity of glass needed, the geometry of the Crystal Palace was derived from the dimensions of the available glass: 10 inches x 49 inches. The 49 inch side forms the hypotenuse of a 2.5:1 triangle who's base is 4 feet. Mirroring this triangle results in the basic 8 foot wide roof gable. (fig. 1 and 2) The gable is repeated 3 times to form the base 24 X24 foot plan grid unit. (fig. 3 and 4) The grid unit was repeated hundreds of times in making the 1848 feet long 456 foot wide building that covered 19 acres. Maintaining the plane of the glass surface while using it to cover the curved transept arch ribs results in the angled patterns of the transcept roof. Striking a line from the center of the transept arch through the start, middle and end of 3 consecutive sash bars as they intersect the centers of the arch ribs and intermediate arch ribs ensures the glass is planar (fig. 5 and 6).