This method allows continuous measurements viscosity and measurements under various shearing stresses. The viscosity is determined by the flow field coefficient, the torque and the rotational frequency. Two types of rotation viscometers are described: viscometer of the Couette type with adjustable revolving crucible and viscometer of Searle type with the crucibel at rest and the plunger revolving. The procedure is specified and typical examples of flow field with formules for calculating (annex A) and a typical rotation viscometer (annex B) are described.