To align the detector in X and Y, scan XDET vs. YDET (say, pixels with a pixel size of 3 or 4 microns). Since the big X detector stage doesn't move very smoothly, you might want to scan YDET vs. XDET instead. There should be no sample inserted (being in the center of a pinhole is fine, of course). Display the signal from segment 8 (the outer ring) and move to the center of the (hopefully) centrosymmetrical pattern (see Fig. 20). You might want to use the "Stern Special" color table, which shows very strong contrast from black to red at the lower end of the intensity range.
The file x1ais_20051028_0038.sm is an example for such a scan.