The metrological performance of rotational viscometers was studied.
Two types of rotational viscometers were investigated.
Reference materials were used to assess their performance.
The types of viscometers studied were a Brookfield type and a rheometer.
The rheometer yielded more exact viscosity values for low viscosities.
At higher viscosity values, both viscometers showed similar metrological behaviors.
Uncertainties of measurement for viscosity were evaluated for both viscometers.