A detailed drawing or a blueprint must show accurately the sizes of openings. The order should be accompanied also by a good description of the space that is to be illuminated, so that the factory experts may select the best prism lenses for the work.

The slab is made up complete, glazed and finished in any desired size to fit the opening. Where more than one slab is required the necessary T bars are cut to proper length and shipped with the slabs.

These slabs can be installed by any workman who will but follow the directions that accompany shipment. The slabs as they come from the factory will be found of perfect fit, ready for the calking of the joints.

In ordering, sizes of openings must be given either by detailed drawings or by blueprint, and the conditions of the space to be daylighted should be described fully in order to secure the proper prism lenses for the best results.