The time required for an air bubble in liquid to rise is directly proportional to its viscosity. Bubble rise rates vary with the inside diameters of viscosity tubes; therefore, the tubes must be precision matched to a tolerance that will keep bubble rise rate variations below the level of visual detection. Any variations in readings are attributed to differences in viscosities. Viscosity tubes can be used by either comparison of the bubble rate rise of the samples to samples of known viscosities or calibrated standards contained in tubes of the same dimensions or by time trials ie the length of time in seconds it takes for a bubble to pass of set distance in the viscosity tube. Viscosity measurement is an important measurement feature in the food, paint, polymer coating and other industries where flow is a critical product or use characteristic.