1.1 This practice specifies the procedure for the calculation of Permanent Shear Stability Index (PSSI) of an additive using viscosities before and after a shearing procedure. 1.2 PSSI is calculated for a single blend component and can then be used to estimate the effects of that component on finished lubricant blends. 1.3 This practice is applicable to many products and may use data from many different test methods. The calculation is presented in its most general form in order not to restrict its use.