SummaryThis paper deals with the formulae, which make possible the calculation of quantities indicating accuracy, defined as follows and used in the “Koninklijke/Shell Laboratorium, Amsterdam”.1The repeatability r represents the greatest difference between two single results that should be considered acceptable if they are obtained within a small interval of time by a competent operator using his set of apparatus in one laboratory.2The reproducibility R(n) represents the largest acceptable difference between the mean of the nAresults of a laboratory and the mean of the nBresults of another laboratory, possibly obtained at widely different times (n=nA+nB