It commonly happens that the detector is not quite perpendicular to the beam normal. In that case, what should be a circular pattern is elongated perpendicular to the tilt axis. The combination of Det-Tilt and Azimuth correct for this. (These options are only used in SAXS mode.) Det-Tilt is the amount that the detector is tilted (in degrees) and Azimuth is the angle with which the pattern is tilted. For a pattern that appears to be stretched along the x-axis, you should set Azimuth=0 and play with Det-Tilt until the pattern is circular. For a pattern that appears to be stretched along the y-axis, Azimuth should be 90. In fact, any value of Azimuth between -360 and 360 is allowed.
This feature also corrects for another problems that some detectors have, which is that the gains in the X and Y direction may not be the same, also resulting in noncircular patterns. In fact, if the X-gain is set too high this is equivalent to a tilt of the detector with Azimuth=0.