A calibration model of multielement methods for simultaneous determination of micro- and macro-concentrations of elements by computing the arc atomic-emission spectra has been developed. A calibration procedure for the analytical line group of the elements to be determined is offered. It allows the lower and upper limits of the concentration range for each line of the determined element to be calculated by means of the least-square method (LSM) and the Weibull distribution law is used to extend the concentration region. The calibration model was successfully tested for different arc optical emission spectroscopy (OES) methods.