In the case of icosahedral Al-Pd-Mn we compare the STM (scanning tunnelling microscopy) image of the real fivefold surface to the STM simulations on the candidates of the fivefold bulk terminations. We make the choice of which termination fits best to the real image. It leads us to some hints important either for the chemistry of the bulk-model or for the eventual correction of the model of atomic positions itself. We work in the frame of the particular model of atomic positions, based on the diffraction data for Al70Pd21Mn9 and Al62Cu25.5Fe12.5. We also discuss the possibilities beyond this model.