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 [15]).