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It will make data reduction more straightforward if the rotator PA is adjusted so that the CCD chip is aligned with the cardinal points. Unfortunately, the rotator PA required is not the same each observing run, since it is possible to mount the detector in more than one orientation.
The simplest method of measuring the required rotator PA is to take a pair of exposures of a star, offsetting the telescope either in RA or dec between the two exposures. Use the DMS to measure the coordinates of the star in the two images, and hence determine the direction in which the star moved on the chip. Then adjust the rotator PA until this direction is aligned with one of the chip axes.