English: Frederick E. Terman's "Universal Resonance Curve", a symmetric approximation to the normalized response of a resonant circuit; abscissa values are deviation from Fc in units of Fc/(2Q), the 3dB-half-bandwidth; ordinate is relative amplitude, and phase in cycles. The upper (green) dashed phase curve is from a system of two poles and no zero, which lags 90 degrees (0.25 cycle) at resonance. The other (red) dashed curves are for a pair of poles with a zero at DC (at s=0 in Laplace notation), which is what is usually approximated by the universal resonance curve, or was in Siebert; in terms of magnitude gain, it is asymmetric in the opposite direction of the green curve. These curves are calculated for a Q value of 4; higher Q values will give curves closer to the universal curve. The X's represent deviations of one half-bandwidth (plus or minus Fc/2Q, the -3dB points), gains of 0.707, and phase shifts of 45 degrees (0.125 cycle).