Dear Bhola kumar Paswan, please have a look at the following free access RG document. My Regards

https://www.researchgate.net/publication/272391655_An_improved_estimation_of_shear_rate_for_yield_stress_fluids_using_rotating_concentric_cylinder_Fann_viscometer

Yield stress is generally determined using model fitting of Fann VG meter data i.e., dial readings and rotor rotation using non-linear regression analysis. For drilling fluid analysis, API RP 13 D also provides detailed methodology to estimate yield stress.

Hello Bhola Kumar ,

Here's a paper which speaks about exactly what you asked: (PDF) Determination of Viscosity and Wall Slip Behavior of a Polymer-Gel Used for Leakage Control From Couette Viscometry Data (researchgate.net)

Article Determination of Viscosity and Wall Slip Behavior of a Polym...

Best regards,

Phil