This software was developed to fit many-parameters IR/Vis/UV transmission curve models of multilayers to measured data. It implements a modified Forouhi2019 model for the complex refractive index of materials, with revised fitting parameters that improve the stability of the fitting and the manual search of initial values. A matrix calculation of the transmission takes in account the interference effects beteween the layers. The implemented GUI allows to easily explore the initial parameters and to fine-tune them, as well as adding model terms.