The straightness accuracy of the move for the stages has been measured with an autocollimator. The straightness is a very important parameter when making raster measurements that are performed with the two stages moving simultaneously. Here, yawing, pitching, and rolling are defined in Fig. 3 with reference to the directions of the x-ray beam and each moving axis. Figure 4 shows the straightness as angle changes of the stages with the position of each moving axis. Note that as for the rolling of each stage (i.e., rotation around some axis with moving along that axis: $SY\u2212\theta Y$, $SZ\u2212\theta Z$, $DY\u2212\theta Y$, and $DZ\u2212\theta Z$), we obtained only its upper limit and it is not plotted in Fig. 4. The yawings of the S and D stages when moving along the $Y$ ($SY\u2212\theta Z$ and $DY\u2212\theta Z$) and $Z$ axes ($SZ\u2212\theta Y$ and $DZ\u2212\theta Y$) are less than 10 arc sec. Meanwhile, the pitchings of the $Y$-axes of the two stages ($SY\u2212\theta X$ and $DY\u2212\theta X$) are larger, and the angular changes along each axis are $\u223c40$ and $\u223c60\u2009\u2009arc\u2009sec$ for $SY\u2212\theta X$ and $DY\u2212\theta X$, respectively. The pitching of the other axes ($SZ\u2212\theta X$ and $DZ\u2212\theta X$) are intermediate and no larger than 30 arc sec. The upper limit of the rolling of the detector $Z$-axis ($DZ\u2212\theta Z$) is somewhat larger and is about 60 arc sec. The limits of the rollings of other axes are 15, 20, and 25 arc sec for the sample $Y$-axis, $Z$-axis, and the detector $Y$-axis ($SY\u2212\theta Y$, $SZ\u2212\theta Z$, and $DY\u2212\theta Y$), respectively.