The high temperature viscometers VIS 403 and VIS 403HF measure the dynamic viscosity of materials with Newtonian behavior such as glasses, slags or mold powder. The instrument operates by measuring the shear stress and shear rate of a rotating bob immersed in a fluid filled cup under controlled temperature. Two different bob and cup configurations are available based on the viscosity of the test fluid. Tests may be conducted in controlled stress or controlled rate conditions, and under isothermal or temperature ramp programs.