Abstract: A Viscometer includes a casing defining therein a chamber and a rotor mounted in the chamber so as to define with the walls of the chamber a space for receiving the liquid whose viscosity is to be measured. Bearing means is interposed between the casing and the rotor is capable of rotational movement about an axis thereof relative to the casing, and means is operable to monitor the deceleration of the rotor when the rotor is rotating under the action of stored kinetic energy against the viscous drag of said liquid, the monitoring means being responsive to at least two of the three variables time, angular distance travelled by the rotor, and angular speed of the rotor.