Secondary Sampling Unit. A secondary sampling unit is a unit or collection of units. In two-stage sampling, we first select PSUs, then we select SSUs within the selected PSUs. In two-stage sampling, the SSUs typically are the units we will measure.
SAYBOLT SECONDS UNIVERSAL. Units of viscosity as measured by observing the time in seconds required for 60ml of a fluid to drain through a tubular orifice 0.483 inches long by 0.0695 inches in diameter at stated conditions of temperature and pressure.