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The relative molecular mass is an important indicator for evaluating the properties of polymers. Among all the methods for determining the relative molecular mass of polymers, the viscosity method is a relative approach; yet due to its simple equipment requirements, wide range of applicable relative molecular masses, and fairly good experimental accuracy, it has become a commonly used experimental technique. Viscosity is one of the important quality parameters of sizing paste; its value affects the rheology, film-forming ability, and adhesion of the paste, which in turn influences quality indicators related to sizing such as the proportion of penetration and coating by the paste during yarn sizing, the sizing rate, and the degree to which fuzz is suppressed. For this reason, textile mills and sizing production plants attach great importance to the viscosity of sizing. Commonly used instruments for measuring slurry viscosity in China include: capillary viscometers (such as Ostwald viscometers and Ubbelohde viscometers), rotational viscometers (such as the A1017 rotational viscometer), Engler viscometers, and falling-ball viscometers. Currently, pulp manufacturers generally use an A1017 viscometer to measure the absolute viscosity of pulp before it leaves the factory, while textile mills use funnels to determine the time required for the pulp to flow, which serves as an indicator of its relative viscosity during actual production. Due to the inconvenience of testing the absolute viscosity of pastes (measured in mPa·s) and the lack of a clear correlation with funnel seconds, textile factories still use the easier-to-operate Engler viscometer to determine the viscosity of starch-based pastes.