Saybolt universal second

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The Saybolt universal second (SUS or SSU) is a measure of kinematic viscosity used in classical mechanics. It is the time that 60 cm3 of oil takes to flow through a calibrated tube at a controlled temperature, 38 degC. The SUS is used for oils with flowing time up to 5600[citation needed] seconds, in the range of low to medium viscosity such as machine oils.

When the flowing time surpasses 5600[citation needed] seconds, Saybolt Furol seconds (SFS or SSF) should be used instead of Saybolt universal seconds. Saybolt Furol seconds is measured with a controlled temperature of 50 degC. The tube diameter in the two scales is such that the Furol viscosity is one-tenth of the universal viscosity:

\text{Saybolt Furol viscosity} = \frac{\text{Saybolt universal viscosity}}{10}

Calculation of the SUS is specified by the ASTM D2161 specification.

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