1. A method for calculating a model spectrum of an object, having a multilayer system, comprising the steps of: calculating the model spectrum with a plurality of wavelengths and a defined number of model intermediate points (N mod ); calculating prior to the execution of the calculation of the model spectrum, the defined number (N mod ) of model intermediate points, wherein for determining the defined number (N mod ) of model intermediate points, the optical thicknesses Ñ·d of the multilayer system are determined beforehand, wherein for all layers of the multilayer system, without the substrate and without the ambient, the mean value of the dispersion n within the predetermined analysis range is calculated and the optical layer thickness is calculated, in particular together with the nominal value of the layer thickness, and subsequently the sum of all optical layer thicknesses is formed.