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Figure 3
Map of a small portion of the imaging detector centered on the true beam position, depicting conditional probability contours for the location of the direct beam, given an input beam position (black dot). This particular input beam position is 0.8 mm from the true value. Probabilities were determined using the projections of reciprocal-space points from one image onto (a) the b axis, (b) all three unit-cell axes, and (c) the top 20 directions identified by Fourier analysis. Panel (d) uses projections of reciprocal-space points from two images collected 90° apart in φ, onto the top 20 directions. The circle in panel (c) shows the largest search radius, 1.2 mm, which could have been used to find the true beam center given the input value. In panel (d) the largest useful search radius is at least 3.3 mm. The crystal is the same as used in Fig. 1[link], with a = 36, b = 65 and c = 84 Å. 1° oscillation exposures were collected with a detector distance of 130 mm and an X-ray wavelength of 1.0 Å.

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