Question: what is the mathematical equation to calculate a viscosity index?
Answer: For Oils of 100 VI and greater U = antilog [log H - N log Y] where Y = kinematic viscosity of oil in centistokes at 100°C. L = kinematic viscosity in centistokes at 40°C of an oil of 0 viscosity index and having the same kinematic viscosity at 100°C as the oil whose viscosity index is to be calculated.