Although anisotropy is inevitable when heat treating glass a major breakthrough took place in the industry in 2016 by developing an in-line anisotropy visualisation equipment. The result is an in-line equipment capable of visualizing and quantifying the level of anisotropy of each single heat treated glass based on the photo-elastic theory. This allows a scientific way of quantifying the level of anisotropy. The methodology and theory is explained allowing to use the photo-elastic theory to evaluate the level of anisotropy of each single heat treated glass and how this allows to guarantee the consistency of the produced glass with an approved mock-up glass in case of a project. An outlook for further development and improvement will be discussed.