Zahn cup #2 viscosity measurement device. A Zahn cup is a stainless steel cup with a tiny hole in the center of the bottom and a long handle. To determine a liquid’s viscosity, the cup is dipped and completely filled, then the time until the streaming liquid first stops flowing (the efflux time) is measured. A conversion table relating efflux time in seconds to viscosity in centistokes is furnished with each cup.
Use larger cup sizes when viscosity is high and lower cup sizes when viscosity is low.