An apparatus and method for measurement of the stress in and thickness of flat glass or curved glass segments is disclosed that uses fluorescence to quickly and accurately ascertain both the thickness of the stress layers and the wall thickness in addition to the stress curve in flat glass or curved glass segments. The apparatus and method may be used to quickly and accurately measure both the stress in and the thickness of flat glass or curved glass segments at a plurality of various locations therein. The apparatus and method are adapted for large scale flat glass or curved glass segment manufacturing, and are capable of high speed measurement of the stress in and the thickness of the flat glass or curved glass segments.