Compare the \eta _{X}(u) values from Eqs. 11.28 \eta _{X}(u,t)\approx P[A(t)\gt u] v_{X}^{+}(0,t)\left\lgroup 1-\exp \left[\frac{-v_{A}^{+}(u,t)}{P[A(t)\gt u]v_{X}^{+}(0,t)}\right] \right\rgroup , 11.30 \eta _{X}(u,t)\approx -v_{A}^{+}(u,t) \left\lgroup 1-\exp \left[ \frac{-v_{A_{1}}^{+}(u,t)}{v_{X}^{+}(u,t)} \right] \right\rgroup \left\lgroup1-\frac{v_{X}^{+}(u,t)}{v_{X}^{+}(0,t)} \right\rgroup ^{-1} with those obtained by other methods in Example 11.4 for a stationary, mean-zero, Gaussian, narrowband process with \alpha _{1}=0.995 .