This International Standard provides a standard basis for the collection and processing of data for the determination of the uncertainties in measurements of discharge in open channels by velocity-area methods using current-meters. To determine the discharge in open channels by the velocity-area method, components of the flow (velocity, depth and breadth) need to be measured. The component measurements are combined to compute the total discharge. The total uncertainty in the computed discharge is a combination of the uncertainties in the measured components. Clause 4 of this International Standard deals with the types of errors and uncertainties involved. Clauses 5 and 6 present a standard procedure to estimate the component uncertainties by the collection and processing of the necessary data. This International Standard is intended to be applied to velocity-area methods that involve measurement of point velocities at a relatively small number of discrete depths and transverse positions in the flow crosssection, as described in ISO 748. This International Standard is not intended to be applied to measurements made by Acoustic Doppler Velocity Profilers (ADVP) or other instruments that produce essentially continuous velocity profiles of the flow field.