The viscosity of a fluid measured at a given shear rate at a fixed temperature.
In order for a viscosity measurement to be meaningful, the shear rate must be stated or defined.
The viscosity of a fluid measured at the shear rate specified by api.
In the bingham plastic rheology model, apparent viscosity (av) is one-half of the dial reading at 600 rpm (1022 sec-1 shear rate) using a direct-indicating, rotational viscometer.
For example, a 600-rpm dial reading is 50 and the av is 50/2, or 25 cp.