A plot of Y/Y₀ against Q₀δ for a series-resonant circuit, or of Z/Z₀ against Q₀δ for a parallel- resonant circuit, where Y and Z are the admittance and impedance of a circuit, Y₀ and Z₀ are the values of these quantities at resonance, Q₀ is the Q value of the circuit at resonance, and δ is the deviation of the frequency from resonance divided by the resonant frequency; it can be applied to all resonant circuits.