Pointing sessions are made every one to two weeks; at present, the fitted pointing parameters yield an absolute pointing accuracy better than (r.m.s.). We also try to keep the receivers as closely aligned as possible (to about , however, alignment can be lost by unknown reason). Checking the pointing and alignment is the responsibility of the observers (use a planet for alignment checks). Normally, the focus position can be monitored with the 3 mm Continuum receiver. Note that 230 G2 and 230 G1 have foci differing by 0.5 mm. Using both receivers, you should carefully monitor the focus and choose a compromise value. Not doing so may result in broadened beams (e.g. HPW and non-gaussian beams on one receiver ).