How does a rotational viscometer work?

Rotational viscometers work by getting the measurements of the torque on a vertical stand that moves the spindle in a rotational direction. The rotation of the spindle is usually proportional to how viscous the sample is. Rotational viscometers are used to measure viscosity. It is common to find most rotational viscometers looking the same, however, two unique and different set-ups are used when measuring viscosity using the rotational viscometer. Below are the two main systems that shows how a rotational viscometer work.