The glass industry has been challenged for many years with creating an optical measurement standard for glass products and windows. Measuring glass distortion, i.e., deviation from flatness, is not a new topic. However, with tighter energy efficiency demands, more variations in glass sizes, code changes and new glazing systems have resulted in more heat-treated glass, double (and even triple) insulating glass units, and multi-ply laminates in use than ever before. All of these products may increase the amount of distortion seen on buildings. Learn more about creating an optical standard and/or number for a glass product. This document was first published in 2018.