The decker selector dial has a micrometer mounted in the centre. This micrometer sets slit width. The scale is in 100s of microns. The whole spectrograph assembly may be rotated, but frequent movement during the night is not recommended as it is rather fiddly. The spectrograph is installed with the slit East-West by default.
Rotation is via a white handset attached to the back of the mirror cell.
Whilst driving the rotator watch all cables carefully. They are usually kept looped up on themselves with plastic ties, so if they are pulling taught, you may need to release them and let them hang free. If you change the slit alignment on the sky, you will need to rotate the autoguider CCD an equal amount in the opposite direction to keep it aligned East-West. This is not an issue at the moment, since the autoguider does not work, but may become one more reason for not using the rotator in the future. It gives a digital display of the focus setting.