A comparison of the extended Shuey approximation to the exact Zoeppritz equations for |${\bf R}^\cup$|⁠. The left-most column shows the 1,1-element, which corresponds to the |$PP$| term. The centre-left column shows the 1,2-element, which corresponds to the |$PS$| term. The centre-right column shows the 2,1-element, which corresponds to the |$SP$| term. Finally, the right-most column shows the 2,2-element, which corresponds to the |$SS$| term. The medium parameters used for the interface correspond to the low-contrast parameters displayed in Table 1. Within each figure, the number of contrast terms |$\Lambda$| taken into account is constant, while the different coloured lines represent the results for different values of N. These results are compared to the true, Zoeppritz equations, which are represented by the solid black lines. Also note the dashed vertical lines, which indicate the maximum angle |$\theta _{max} = 0.8 \cdot \theta _c$| up to which the approximation holds.