Combined relationship for GLO and GAL models together. Left panel: I_e-R_e plane in which the combined relation is shown against the observational data of Burstein et al. (1997). Right panel: corresponding 3DKS for the same models. In both panels, the meaning of the symbols is the same as in previous figures. No particular remarks are to be made here, aside from noting a general agreement between data and theory. The kind of SFH we have adopted seems to be compatible with the overall observational situation.