Z' Reservation at LEP2

We consider the possibility that one extra $Z\equiv Z'$ exists with arbitrary mass and fermion couplings that do not violate (charged) lepton universality. We show that, in such a situation, a functional relationship is generated between the \underline{deviations} from the SM values of three leptonic observables of two-fermion production at future $e^+e^-$ colliders that is completely independent of the values of the $Z'$ mass and couplings. This selects a certain region in the 3-d space of the deviations that is \underline{characteristic} of the model ($Z'$ "reservation"). As a specific and relevant example, we show the picture that would emerge at LEP2 under realistic experimental conditions.