The standard lays down a procedure for the determination of the uncertainty of a measuring result, when the quantity of interest is not measured directly, but calculated from other measured quantities by means of mathematical equations. The procedure is a generalized form of the error propagation law of Gauss; it uses a covariance matrix which serves as a measure of the uncertaintly. The procedure provides a consistent treatment of the uncertainties of the individual measured quantities and of other data (e.g. taken from literature) as well as the consistent further treatment of the measuring result.