The BF35 Viscometer measures viscosity of oil drilling and fracturing fluids at atmospheric pressure in both field and laboratory settings. The primary application for this instrument is in the oil/gas drilling industry to measure viscosity of drilling muds and fracturing fluids according to established methods from the American Petroleum Institute and the ASTM.

The BF35 operates on a different measurement technique than traditional standard Brookfield Viscometers. The sample is placed in the cup and the spindle/chamber combination is then immersed into the sample. When the motor is turned on, the chamber rotates while the spindle remains stationary. When the dial reading becomes stable, the torque reading is recorded and manually converted into a viscosity value in centipoise.