BS 7034-4-1988 Glass viscosity and determination of viscosity fixed points. Method for determining viscosity using beam of light bending is a standard developed by the British Standards Institution, which specifies a method for measuring the dynamic viscosity of Glass by beam of light bending. This method is suitable for measuring the viscosity of Glass at high temperatures. The dynamic viscosity of Glass is calculated by applying a load to a rod-shaped specimen (called a beam) supported at both ends and measuring its viscous deflection rate at a given temperature. This method is suitable for glass materials with viscosities ranging from 10 Pa · s to 10 ¬ ³ Pa · s, and is widely used in glass production, research and development, and quality control. It provides a scientific basis for the evaluation of high temperature rheological performance of Glass.