This Gulf standard sets out the method and means for initial and subsequent verifications of glass capillary viscometers (ordinary instruments), free liquid flow, intended for the measurement of kinematic viscosity of liquids. The principle of verification consists in determining the constant of the viscometer, using a suitable and stable reference material of viscosity, the viscosity of which was measured using standard or reference viscometers. The operations making it possible to determine the viscosity of the reference materials of viscosity and the constant of the viscometer should be carried out simultaneously, in the same thermostatic bath. It is however admissible to carry out the verification of viscometers using reference materials of which the values of viscosity have been given by another laboratory. The verification of viscometers shall then be carried out at the temperature of measurement of the viscosity of the reference materials in question. Other verification methods are accepted provided that they give similar results