Viscosity is measured with various types of viscometers and rheometers. These values are used for calibrating certain types of viscometers. The viscosity is reported in Krebs units (KU), which are unique to Stormer viscometers. Vibrating viscometers can also be used to measure viscosity. Rheometers and viscometers work with torque and angular velocity. Resonant, or vibrational viscometers work by creating shear waves within the liquid. Viscometers only measure under one flow condition. Such viscometers can be classified as direct-flow or reverse-flow. Vibrating viscometers are rugged industrial systems used to measure viscosity in the process condition. "Cone and plate" viscometers use a narrow-angled cone in close proximity to a flat plate. Viscometers that can characterize non-Newtonian fluids are usually called "rheometers" or "plastometers".