The grating is removed by opening up the two blue access hatches in the centre of WYFFOS, and pressing (and holding) the white button until the grating turns to its access position. A further press of the button will unclamp the grating. The grating can then be changed. When the new grating is put in, press the button again and the clamps should engage. Put the panel back on, making sure it is clipped securely. If it isn't, there will be a warning on the ICL mimic in the control room and you won't be able to change the grating angle. The gratings are the normal ISIS gratings and are kept in the usual place on the observing floor. If you change a grating, you must update this using the ICL wchange command.