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The camera-dewar assembly can be rotated, using two push-pull micrometers, to align the spectrum with the chip. For best sky subtraction, it is preferable to align the projected spectrograph slit along columns. Note that this does not guarantee that the dispersion will be perfectly aligned along rows (there is no grating rotational alignment adjustment). Any small dispersion misalignment can be taken out in the data reduction process. Since some gratings are slightly misaligned in their cells, this alignment should be checked after each grating change.
Check the alignment using the observation taken for the best focus above. Plot column 1000, then over-plot column 2000 using implot. If the spectra are not aligned one may have to adjust the dewar rotation. The HENEAR lamp should be used for alignment of spectral lines along columns.