Viscometer is an instrument used to measure the viscosity of a fluid.

Each of the Laboratory Viscometers/ Rheometers is supplied with an internal spring used to calculate the viscosity of a material. These springs have different measuring capabilities:

LV is for low viscosity materials and can measure the thinnest materials. Typical examples include inks, oils, and solvents.
RV is for medium viscosity materials than those measured with an LV torque. Typical examples include creams, food, and paints.
HA is for higher viscosity materials than those measured with an RV torque. Typical examples include gels, chocolate and epoxies.
HB is for even higher viscosity materials than those measured with an HA torque spring.  Typical examples include asphalt, caulking compounds, and molasses.

There are different types of viscometers. The most popular is Rotational viscometer, U-tube viscometer and falling ball viscometer.

Choice of the instrument depends on the project and fluids used by the laboratory.

U-Tube Viscometer